

































































































WORKS OF JAMES H. FUERTES 

PUBLISHED BY 

JOHN WILEY & SONS. 


Water and Public Health. 

The Relative Purity of Waters from Different 
Sources. i2mo, x -f- 75 pages, 68 figures, cloth, 
Si.50. 

Water Filtration Works. 

121110, xviii + 283 pages, 45 figures and 20 half-tone 
plates, cloth, S2.50. 







Cleaning the Sedimentation Basins at St. Louis, Mo. 

Frontispiece. 










WATER FILTRATION WORKS. 


BY 

JAMES H. C FUERTES, 

Member of the American Society of Civil Engineers. 


FIRST EDITION . 

FIRST THOUSAND. 


» » 

) ) > 
) «> 

r i t 

j , * 


NEW YORK: 

JOHN WILEY & SONS. 

London : CHAPMAN & HALL, Limited. 

1904. 


‘F9& 


Copyright, 1901, 

BY 

JAMES H. FUERTES. 


Gif 

Sidney r : 

Oct. 31 


HU 


>3b 



ROBERT DRUMMOND, PRINTER, NEW YORK. 


3 “ 



PREFACE. 


In 1839 James Simpson built a set of filters for 
the Chelsea Water Company at London. These 
filters, the first constructed for the purification of a 
municipal water-supply, were intended merely to 
clarify the water, no investigations, at that date, 
having been made to determine what results, other 
than clarification, could be obtained by filters prop¬ 
erly designed and operated. Twenty-seven years later 
Mr. James P. Kirkwood visited Europe for the city 
of St. Louis for the purpose of studying the methods 
of filtration in use abroad. On his return he sub¬ 
mitted a report in which the filtering of the St. Louis 
water was recommended, following this report in 1869 
with a treatise on the “ Filtration of River Waters.” 
This book contained the results of his observations 
and studies of thirteen filter-plants in Europe, and was 
the first publication to appear in English on the sub¬ 
ject of filtration. Able as was this discussion, how¬ 
ever, public interest in the question of the purification 
of polluted waters remained dormant in the United 



vi 


PREFA CE. 


States until the results of the valuable experimental 
work conducted at the Lawrence Experiment Station 
were published in the Annual Reports of the Mas¬ 
sachusetts State Board of Health. These reports 
attracted world-wide attention, cleared up many 
points that had been but imperfectly understood in 

f 

the phenomena attending filtration, and gave a stimu¬ 
lus to public interest which has resulted in the estab¬ 
lishment of many filter-plants in the United States, as 
well as in other countries. With the exception of 
the above-named works, and the authoritative and 
useful book published in 1895 by Allen Hazen, en¬ 
titled “The Filtration of Public Water-supplies,” 
the most valuable data bearing upon the subject of 
filtration are to be found in the not generally accessible 
reports of special investigations, in the current techni¬ 
cal journals in the United States and Europe, and in 
a few works on the purification of water, which treat 
the subject principally from the sanitary and chemical 
points of view. The author has drawn freely upon 
these sources of information, particularly upon the 
valuable Annual Reports of the Massachusetts State 
Board of Health, and the reports on the purification 
of the Washington, Pittsburgh, Cincinnati, Louisville, 
and Providence water-supplies. Persons familiar with 
the reports of the Massachusetts State Board of Health 
will recognize in the first pages of the chapter on The 
Theory of Slow Sand-filtration the substance of the 
very clear statement of the phenomena attending 
decay and regeneration written by Dr. Thomas M. 
Drown to whom full acknowledgment is tendered. 


PREFA CE. 


Vll 

Among his professional colleagues who afforded 
him opportunities of visiting the plants under their 
direction and also furnished him with many valuable 
data concerning the construction and operation of 
filtration works, the author wishes specially to men¬ 
tion the late F. Andreas Meyer, City Engineer of 
Hamburg; Wm. H. Lindley, Civil Engineer, Frank* 
fort-on-the-Main, Germany; M. Peter, City Engineer, 
and M. Bertschinger, City Chemist, Zurich; Director 
Beer and Superintendent Engineer Anklamm, Berlin, 
and Wm. Anderson, Treasurer and General Manager 
of the Edinburgh Water-works. 

The author is also under obligations to Mr. William 
Wheeler, Consulting Engineer, Boston, for the photo¬ 
graphs of the Ashland, Wis., and Somersworth, N. H., 
covered filters; to Mr. Geo. I. Bailey, Superintendent 
Bureau of Water, Albany, for valuable data and for 
the photographs of the Albany filters; to Mr. Edward 
Flad, Water Commissioner, St. Louis, Mo., for the 
pictures of the Intake and Settling Basins of the St. 
Louis Water-works; to Mr. Morris Knowles, Assistant 
Engineer in charge of the Testing Station, Philadel¬ 
phia, for the photographs reproduced in Plates XI, 
XVI, XVII, XVIII and XIX; and to the New York 
Continental Jewell Filtration Company for valuable 
data, and for the illustrations forming Plate XV and 
Figs. 37 to 45 inclusive. 

During the past decade great advances have been 
made in the development of processes for the purifi¬ 
cation of polluted waters. These processes, and the 
works necessary for carrying them out, are described 


Vlll 


PREFA CE. 


with sufficient fulness in the following pages to indi¬ 
cate the results that may be attained in the matter of 
the purification of polluted waters, the means of at¬ 
taining these results, and the elements entering into 
the design, as well as into the cost of the necessary 
works, both as regards construction and operation. 

James H. Fuertes. 


New York, April , 1901. 


TABLE OF CONTENTS. 


CHAPTER I. 

INTRODUCTORY. 

PAGE 

Water and Public Health. i 

Typhoid Fever and Water-supply. i 

The purification of Water by Natural Agencies. 3 

Effects of Aeration. 4 

Effects of Storage on the Quality of the Water. 5 

Effects of Mud Deposits in Reservoirs on the Quality of 

the Water. 6 

Effects of the Fouling of Water-mains on the Quality of 

the Water. 9 

Self-purification of Streams. 12 

Effect of the Freezing of Water on its Quality. 12 

The Protection of Water-supplies. "13 

Permissible Pollution. 13 

Legal Protection of Water-supplies. 13 

Provisions for Betterment of Water-supplies. 14 

Requirements of Water Companies in the Matter of Pro- 

• tection. 15 

Protection of Surface Supplies. 15 

Ownership vs. Legal Protection. 17 

Effects of Surface Washings. 17 

Protection from Sewage Pollution. 22 

Protection of Lake Supplies. 23 

The Purification of Water by Filtration. 25 


IX 






















X 


TABLE OF CONTENTS . 


CHAPTER II. 

INTAKES, SEDIMENTATION, AND SETTLING BASINS. 

PAGE 

Intakes. 28 

Tidal Streams. 28 

Rivers with Stable Banks above Flood Height, and with 

small Range of Fluctuation of Level. 29 

Rivers with Stable Banks below Flood Height. 30 

Rivers with Shifting Banks and Bottoms, and Great 

Range of Fluctuation of Level. 33 

Sedimentation. 33 

Amount, Character, and Distribution of Sediment. 33 

Turbidity. 36 

Standards of Measurement . 36 

Rate of Sedimentation. 37 

Effects of Winds.. 39 

Effects of Temperature. 40 

Effects of Light. 40 

Use of Chemicals to Aid Sedimentation. 41 

Results to be Obtained by Sedimentation. 41 

Efficiency of Sedimentation. 42 

Settling Basins. 45 

Designing. 45 

Location. 45 

Capacity. 46 

Depth. 47 

Length. 48 

Velocity of Flow Through Basins. 48 

Form of Basins. 51 

Arrangements to Draw Off Water Longest in Storage 51 

Locations of Inlets and Outlets. 52 

Construction. 53 

Bottoms. 53 

Underdrainage. 55 

Sides. 55 

Regulating Apparatus. 56 

Removal of Sediment. 60 

Roofing. 61 

Cost. 62 



































TABLE OF CONTENTS. XI 

PAGE 

Operation. 63 

Rate of Flow Through Settling Basins. 63 

Amount of Sediment to be Expected.. 64 

Depth of Sediment to be Provided for. 66 

Periods of Cleaning. 66 

Amount of Water Necessary for Cleaning. 67 

Methods of Cleaning. 71 

Cost of Removing Sediment.. .. 72 

Relative Advantages of the Fill-and-Draw and the 
Continuous Methods of Operation. 73 

CHAPTER III. 

THE PURIFICATION OF WATER BY SLOW SAND-FILTRATION. 

Introduction. 75 

Types of Filters Used for Municipal Supplies. 75 

Slow Sand-filtration. 76 

Rapid Sand-filtration. 76 

Theory of Slow Sand-filtration. 77 

Action of Slow Sand-filters. 80 

Bacterial Efficiency. 81 

Bacterial Purification. 81 

Hygienic Efficiency. 81 

Influence of Character of Water. 82 

Influence of Size and Character of Sand. 84 

Influence of Compacting of Sand Layer. 84 

Influence of Depth of Sand Layer. 86 

Influence of Loss of Head. 90 

Influence of Depth of Water on Filter Surface. 93 

Influence of Rate of Filtration. 93 

Influence of Sudden Change of Rate. 95 

Influence of Age of Filters. 96 

Influence of Scraping. 97 

Influence of Method of Application of Water to Inter¬ 
mittent Filters. 99 

Influence of Method of Putting Filters in Service after 
Scraping. 100 
































Xll TABLE OF CONTENTS, 

PAGE 

Influence of Temperature. ioo 

Conclusions. ioi 

CHAPTER IV. 

THE DESIGN, CONSTRUCTION AND OPERATION OF SLOW SAND-FILTERS. 

Designing. 103 

Per Capita Water Consumption and Waste Reduction.... 103 

Number of Filter beds Required. 107 

Excess Area Required. 107 

Location and Grouping of Beds. 113 

Shape of Beds. 115 

DepthofBeds. 117 

Construction.=. 117 

Preparation of Site. 117 

Side Slopes and Bottoms. 117 

Precautions to Prevent Water Passing to the Under¬ 
drains in an Unfiltered State. 119 

Effects of Sun on Paving of Open Beds. 119 

Covered vs. Uncovered Filters. 120 

Drainage of Roofs. 130 

Ventilation. 133 

Tramways for Sand Haulage. 134 

Bottoms and Forms of Same. 134 

Underdrains.... . 139 

Gravel Layers. 142 

Filter-sand. 146 

Depth. 149 

Character of Sand. ico 

Placing Sand. 153 

Placing Gravel. 153 

Structural Details. 134 

Sand Washing. J54 

Regulating Apparatus. !6 j 

Cost of Slow Sand-filters. 174 

Operation. x 7g 

Relative Locations of Filters and Filtered-water Reser¬ 
voirs. x 7g 

































TABLE OF CONTENTS . xiii 

PAGE 

Scraping Filter-beds. 180 

Cost of Scraping. 183 

Frequency of Scraping. . 185 

Effects of Covers on Frequency of Scraping. . 187 

Transporting Sand to Washers. iqo 

Cost of Sand Washing. 190 

Quantity of Water Used for Sand Washing. 197 

Loss of Sand in Washing. 198 

Ice on Open Filters. 198 

Refilling Filters after Scraping. 199 

Double Filtration. 200 

CHAPTER V. 

THE PURIFICATION OF WATER BY RAPID SAND-FILTRATION. 

Theory of Rapid Sand-filtration. 201 

The Coagulant and its Effect on Efficiency of Filtration.. 201 

Quantity of Coagulant Required. 203 

Time of Admixture of Chemical. 207 

Effect of Filtering Medium. 210 

Effect of Rate of Filtration. 211 

Effect of Loss of Head. 213 

Effect of Washing Filters. 214 

Effect of Trailing... 215 

CHAPTER VI. 

THE CONSTRUCTION AND OPERATION OF RAPID SAND-FILTERS. 

Gravity and Pressure Filters. 217 

Introduction of Chemical Solution. 225 

Regulating Apparatus. 231 

Washing Arrangements. 234 

Cost of Rapid Sand-filters. 238 

Operating Rapid Sand-filters. 242 

Period of Time Between Washings. 242 

Lost Sand. 243 





























xiv TABLE OF CONTENTS. 

FAGB 

Labor for Operating Rapid Sand-filters. 243 

Quantity of Water Required for Washing and Rate of Appli¬ 
cation of Wash-water. 244 

Wasting Wash-water.... 245 

CHAPTER VII. 

CONCLUSIONS. 

General. 246 

Combinations of Rapid and Slow Sand-filters. 247 

The Anderson Process. 249 

The Pasteur-Chamberland Process. 250 

The Fischer or Worms Process. 250 

The Maignen Process. 255 

CHAPTER VIII. 

FILTERED-WATER RESERVOIRS. 

Location. 256 

Shape. 256 

Circulation. 257 

Capacity. 257 

Depth. 260 

Effect of Pumping on Depth. 261 

Bottoms. 262 

Workmanship. 263 

Walls. 265 

Covers. 266 

Ventilation. 267 






















LIST OF FIGURES 


FIG * PAGE 

1. Rate of Subsidence of Mississippi River Water at St. Louis, 

Mo. 38 

2. Rate of Clarification of Mississippi River Water at St. Louis, 

Mo., in Passing Slowly Through a Long Flume. 44 

3. Effect of Size of Sand Grain on Efficiency of Slow Sand- 

filtration. 86 

4. Diagram Showing Retention of Bacteria and Nitrogen in Ten 

Slow Sand-filters, at the Lawrence Experiment Station ... 88 

5. Arrangement of the Lake Mueggel Filter-plant, Berlin, Ger¬ 

many... 114 

6. Plan of Berlin (Mueggel) Filter-bed. 116 

7. Groined Arches. 122 

8. Masonry Groined Arches with Arch Ribs. 123 

9. Concrete Groined Arches... 124 

10. Domed Covering with Arch Ribs. 127 

11. Cylindrical Arches. 128 

12. Flat Domes. 129 

13. Concrete Domed Construction. 130 

14. Typical Plan and Sections of Covered Slow Sand-filter. 137 

15. Plan of Filter-bed, Zurich, Switzerland. 138 

16. Conversion Diagram. Gallons per Day into Cubic Feet per 

Second and per Minute, and Gallons per Second. 140 

17. Conversion Diagram. Million Gallons per Acre into Gallons 

per Square Yard, Gallons per Square Foot, and Vertical 
Depth in Feet. 141 

18. Conversion Diagram. Million Gallons per Acre per Day for 

Different Areas into Cubic Feet per Second. 142 

19. Diagram Showing Frictional Loss of Head in Pipes. 143 

20. Hollow Floor, Zurich Filters. 144 


xv 






















XVI 


LIST OF FIGURES . 


FIG. PAGE 

21. Diagram Showing Head of Water Consumed in Passing 

Horizontally Through Gravel Layers... 145 

22. Cross-section Through Ejector Sand-washer. 158 

23. Plan of Ejector Sand-washer. 158 

24. Longitudinal Section Through Ejector Sand-washer. 158 

25. Regulating Apparatus in Use at Yokohama, Japan.. 162 

26. Regulator in Use at Koenigsberg, Germany. 163 

27. Regulator Designed by Henry C. Gill, and Used at the Berlin 

Filter-plants. 164 

28. Regulator Recommended by James P. Kirkwood for St. Louis 166 

29. Regulating Apparatus in Use at Hamburg, Germany. 166 

30. Regulating Apparatus Designed by Allen Hazen for the 

Albany Filters. 167 

31. Regulator in Use in Zurich, Switzerland. 169 

32. Regulator Designed by Wm. H. Lindley for the Filters at 

Warsaw. 169 

33. Regulator Suggested by the Mayor’s Expert Water Commis¬ 

sion, Philadelphia. 170 

34. Regulator Designed by the Author for the Tome Institute 

Filters. 171 

35. Regulator in Use at Worms, Germany. 173 

36. Regulator in Use at Tokio and Osaka, Japan. 173 

37. Sectional View of Jewell Subsidence Gravity Filter. 220 

38. Plan of Continental Gravity Filter. 223 

39. Sectional Elevation of Continental Gravity Filter. 224 

40. New York Sectional-wash Gravity Filter. 225 

41. New York Sectional-wash Pressure Filter.226 

42. Typical Chemical Solution Measuring Tank for Gravity 

Filter. 227 

43. Chemical Solution Measuring Tank for Pressure Filter. 228 

44. Chemical Solution Pump for Either Gravity or Pressure 

Filters. 230 

45. Weston’s Automatic Controller for Rapid Sand-filters.231 


























LIST OF PLATES. 


PAGE 


Frontispiece. Cleaning the Sedimentation Basins at St. Louis, Mo. 

I. Removal of 30 years’ accumulations of mud from the 

Mt. Airy Reservoir, Philadelphia. 7 ✓ 

II. Intake of St. Louis, Mo., Water-works. 31 

III. Settling Basin, Albany, N. Y. View showing aerating 

inlets for raw water, slope paving, concrete bottom, 
and method of removing sediment. 57 

IV. Albany Filtration Plant. General view of Settling Basin, 

showing removal of sediment deposited from the water 69 

V. Interior view of Ashland, Wis., Covered Filter. First 
adaptation in the U. S. of the groined arch for filter- 


covers. 125 

VI. Somersworth, N. H., Covered Filters. Birdseye view of 

centering for groined arches. 131 

VII. Somersworth, N. H., Covered Filters. View taken dur¬ 
ing construction. 135 


VIII. Somersworth, N. H., Covered Filters. View showing 

the underdrains and gravel being placed in position... 147 

IX. Interior view of Ashland, Wis., Covered Filters, taken 

when the filtering sand was being placed in position... 151 

X. Interior view of Somersworth, N. H., Covered Filters, 
showing the filtering sand being placed in position in 
three layers, the underdrains, and gravel surrounding 


them. 155 

XI. Method of scraping slow sand-filters. 181 ^ 

XII. Albany Filtration Plant Wheeling out sand removed 

from filter after scraping . 191 

xvii 












XV111 


LIST OF PLATES 


PAGE 

XIII. Albany Filtration Plant. Sand-washers as originally 

built. The dirty sand was wheeled in barrows to the 
washers. 193 

XIV. Albany Filtration Plant. Improvement in sand-washing 

machinery. The dirty sand is conveyed to the wash¬ 
ers through a pipe by a portable ejector-hopper and a 

stream of water. 195 

XV. Interior view of East Albany Filter Plant. 221 

XVI. Agitator, Jewell Filter. 235 

XVII. Agitator, Warren Filter. 239 

XVIII. Worms or Fischer Plate ready to be placed in filter. 251 

XIX. Broken Worms or Fischer Plate, showing interior cavity 353 










WATER FILTRATION WORKS. 


CHAPTER I. 

INTRODUCTORY. 

WATER AND PUBLIC HEALTH. 

Typhoid Fever and Water-supply .—The purity of wa¬ 
ter depends upon its source and upon the polluting 
and purifying influences to which it has been sub¬ 
jected. It is now well known that in a community 
using water polluted with sewage the general health 
tone gradually falls lower and lower and its death rate 
increases proportionately. Among the diseases 
known to be capable of transmission by drinking-wa¬ 
ter, typhoid fever holds a prominent position. As it 
is nearly always present in cities, its continued preva¬ 
lence, in abnormal proportions, indicates excessive 
pollution, by sewage or fecal matter, of the drinking- 
water supplied to the community. This is well set 
forth in Table I, in which the death rates are the 
averages for several years: 



2 


WA TER FILTRATION WORKS. 


TABLE I. 


Kind of 
Water Used. 

City. 

Source of Supply. 

Typhoid-fever 
Death Rate, 
per 100,000 People 
per Annum. 


- 

Hague 

From sand dunes 

4-7 

Pure 


Munich 

Mountain springs 

6.0 

water 


Dresden 

Ground-water 

6.0 



Berlin 

Filtered water 

7.0 



Washington 

Potomac R. and wells 

71.0 



Louisville 

Ohio River 

74 0 

water 


Pittsburgh 

Allegheny River 

84.0 


It is also probable that there is a relationship be¬ 
tween the annual typhoid-fever death rate in a city 
and the kind and amount of pollution of its water-sup¬ 
ply. This is indicated in Table II, the data for which 
have been compiled from the records of a great many 
cities. While the figures are, of course, approximate, 
there is sufficient reasonableness in the averages to 
entitle them to consideration. 


TABLE II. 


Kind of Water Used. 

Pure mountain springs. 

Properly filtered water. 

Pure ground-water. 

Protected impounded supplies 

Large normal rivers. 

Large lakes. 

Upland streams. 

Polluted supplies. 


Average Typhoid-fever 
Death Rate per 100,000 
People per Annum. 

. 6 

. 12 

. 18 

. 25 

. 28 

. 39 

. 44 

- 70-300-f 


Basing calculations on the above averages, it will 
be seen that, considering the water furnished by 
mountain springs as the purest obtainable for a city’s 




















IN TROD UCTOR Y. 


3 


supply, and expressing the average annual typhoid- 
fever death rate of a city using such water by i per 
100,000 living, the average rate in cities using other 
kinds of water would be multiples of this in about the 
following ratios: 


TABLE III. 


Kind of Water Used by the City. 

Pure mountain springs. 

Properly filtered water. 

Pure ground water. 

•Protected impounded supplies 

Large normal rivers. 

Large lakes. 

Upland streams.. 

Polluted supplies . 


Comparative Annual Typhoid- 
fever Death Rate. 

. I 

. 2 

. 3 

. 4 

. 5 

.6 

. 7 

. 10-30 


Thus, for instance, the typhoid-fever death rate in 
a city supplied with water from upland streams, with¬ 
out large storage reservoirs, would be expected to be 
about seven times as great as if the water-supply were 
from pure mountain springs; and the filtration of such 
water would, on the average, prevent about three 
fourths of the typhoid-fever deaths. 


THE PURIFICATION OF WATER BY NATURAL AGENCIES. 

In polluted waters a considerable amount of 
purification may take place from natural causes. 
Among these are sedimentation, chemical changes, 
the action of certain vegetal growths in promoting 
sterilization,* and the action of certain bacteria to- 


* See page 1S8 











4 WATER FILTRATION WO RETS. 

ward liquefying and nitrifying the organic matter 
present in the water. 

Aeration .—The aeration of water, by passing it over 
cascades, or falls, is popularly supposed to do much 
toward its purification. The greatest fields of useful¬ 
ness for this treatment, however, are for the oxidation 
of iron in solution; the removal of disagreeable gases; 
the prevention of stagnation, and the retardation of 
the growth of certain forms of vegetal life in the wa¬ 
ter, which, by their development, impart disagreeable 
odors and tastes. 

The waters from the deep wells in New Jersey fre¬ 
quently contain iron in sufficiently large quantities to 
give them a disagreeable taste and to render them 
unfit for use for many purposes. These troubles may 
often be removed by simple aeration accompanied by 
a rapid filtering process to remove the iron salts. 
Quite extensive plants of this kind are in operation at 
Atlantic Highlands and Asbury Park. If the iron is 
present in the form of sulphates, however, simple 
aeration is not so effective, and a treatment of the wa¬ 
ter by the addition of milk of lime, followed by aera¬ 
tion and rapid filtration, proves successful. This 
treatment was resorted to at Reading, Massachusetts. 

At Koenigsberg, Germany, the water supplied to 
the city is allowed to flow about five miles in a natu¬ 
ral watercourse to effect the removal of the iron. 
The iron is deposited on the bottom and the water 
issues, clear and bright, at the lower end of the open 
channel. 

Generally speaking aeration is ineffective except 


INTROD UCTOR Y. 


5 


for the purposes stated; sometimes it may even have 
the opposite effect to purification. For instance: In 
1897 Professor Albert R. Leeds found that aeration 
of the Brooklyn water favored the growth of Aste- 
rionella, an organism that has caused much trouble, 
at certain seasons, by imparting a very disagreeable 
taste and odor to the water. In this case it was found 
that the multiplication of Asterionella was favored, 
essentially, by abundant access of light; by a gentle 
tremulous motion of the water; by the absence of 
peaty or other coloring matter in the water, and by 
storage in shallow reservoirs, together with the pres¬ 
ence of silica and nitrogenous food matter. So far as 
was known, the only remedy which proved effectual 
was the exclusion of light. In order to avoid this 
trouble, in the case of the Brooklyn water, a by-pass 
was provided, so that the reservoirs in which Aste¬ 
rionella caused most trouble could be cut out of the 
distribution system temporarily if necessary. 

Effects of Storage .—Ground-waters and filtered wa¬ 
ters should generally be stored in dark reservoirs, and 
should be delivered to the consumers as quickly as 
possible, as they nearly always deteriorate during 
storage and upon exposure to light. Surface waters, 
however, are frequently improved in quality by stor¬ 
age in large, deep reservoirs, particularly if the reser¬ 
voir sites have been cleared of vegetation and top 
soil before the reservoirs are filled, and if the feeding 
streams are somewhat turbid. Under these condi¬ 
tions the polluting matter washed into the reservoirs 
is greatly dispersed; from 75% to 90% of the sus- 


6 


WA TER FILTRATION WORKS. 


pended matter, together with, often, as much as 
80% to 90% of the microscopic vegetal and animal 
organisms, settles to the bottom and the water is left 
nearly free from turbidity and objectionable qualities. 
The absence of decomposing organic matter in the 
bottom of the reservoir, if stripped, deprives the 
water of the nitrogenous and carbon compounds nec¬ 
essary to support the life of these microscopic organ¬ 
isms, and, hence, they will not multiply rapidly. 
Light is necessary to promote the growth of most 
organisms, but to certain forms it is fatal. Janowski 
demonstrated that gelatine freshly inoculated with 
typhoid germs developed colonies in the dark in three 
days, in diffused daylight in five days, but that in 
strong sunlight the gelatine became sterile in six 
hours. 

Effects of Mud Deposits .—Deposits of mud in stor¬ 
age reservoirs are not necessarily harmful. In Phila¬ 
delphia, when the Lehigh basin was emptied in 1886, 
an analysis of the water covering the mud showed no 
injurious constituents. The same results were ob¬ 
tained at the Fairmount reservoir, when emptied re¬ 
cently to permit the making of repairs, and also at the 
Mt. Airy basin, which had not been cleaned for thirty 
years, and contained from four to five feet of mud. 

Plate I shows this reservoir when the mud had been 
partially removed. 

Such deposits in shallow reservoirs may, however, 
by furnishing proper food, encourage growths of or¬ 
ganisms that will by their development impart dis¬ 
agreeable tastes and odors. Mr. George C. Whipple, 




































- 





























JH Hi 




































IN TROD UCTOR Y. 


9 


Director of the Mt. Prospect Laboratory of the 
Brooklyn Water-supply, and D. D. Jackson, chemist, 
have found that such was the case in some of the 
Brooklyn Reservoirs,* and have recommended, as a 
remedy, the cleaning of the reservoirs early in the 
spring and late in the summer. 

Effects of the Fouling of Water-mains .—The fouling 
of the water-mains in Philadelphia, by deposits in 
them and by growths on their interior surfaces, was 
considered by some people the cause of the poor 
quality of the water; and considerable pressure was 
brought to bear to have the mains cleaned, in order to 
increase the quantity of water they would deliver 
and also to improve its quality. The available data 
concerning the effects of the fouling of water- 
mains rather strongly indicate that the quality of 
the water improves in its passage through the dis¬ 
tribution pipes. Mr. George C. Whipple found that 
during the passage of surface waters through pipe 
lines in Boston there was a considerable reduction in 
the number of organisms, due to sedimentation, dis¬ 
integration, decomposition and consumption by other 
organisms; that there was also a similar decrease in 
the number of bacteria, except during periods of the 
year when decomposition was going on in the pipes, 
and that by their decay the growths tended to pro¬ 
duce bad odors and tastes. These rank growths are 


* Asterionella; its Biology, its Chemistry, and its Effects on 
Water-supplies. Geo. C. Whipple and D. D. Jackson, Journal of 
the New England Water-works, Assn., Vol. XIV, No, x* 




10 


WA TER FILTRATION WORKS. 


not found in pipes carrying filtered water, or ground- 
water free from microscopic forms, as such waters do 
not furnish the necessary food-supply. 

Incrustation is generally greatest with clear, bright 
waters because they contain much oxygen and car¬ 
bonic acid which, in the absence of mineral matter, are 
left free to attack the pipes. When pipes become se¬ 
riously incrusted, so that their capacity is reduced, 
they may either be cleaned or duplicated. The clean¬ 
ing of large mains is done with a scraper, a steel tool, 
which is inserted in the pipe and forced through by the 
pressure of the water. Pipes smaller than five inches in 
diameter cannot be readily cleaned in this way unless 
the pressure is very high. The cleaning is generally 
done in the night-time, when there is little noise from 
traffic, as the movement of the scraper in the main 
must be located by the noise it makes in remov¬ 
ing the blisters. 

The scraping of small pipes, by hand, is said to cost 
on the average about one cent per foot per inch of 
diameter. 

The cost of cleaning several large water-mains, in¬ 
cluding labor, the cost of putting in special manholes 
for entering the scraper, etc., is given in Table IV. 

The danger of using lead pipe with very soft water 
is well recognized. In such waters there is often 
enough free acid to attack the lead and thus form 
poisonous salts. The following case was reported in a 
recent number of the Gcsundheits-Ingenieur. Water, 
was brought in a lead pipe to a forester’s lodge, at a 
certain bathing resort in Germany, from a spring 


IN TROD UCTOR Y. 


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12 


WATER FILTRATION WORKS. 


about two hundred feet distant. On investigation it 
was shown that the plumber, when soldering the 
joints, had allowed a lot of lead filings to remain in 
the pipe. The daughter of the forester became ill 
some days after the completion of the work, the ill¬ 
ness proving fatal shortly afterward. A post-mortem 
examination demonstrated the presence of lead in sev¬ 
eral of the organs of her body, and the water, which 
was very pure at the spring, was found to contain 
0.95 mg. of dissolved lead per litre. 

Self-purification of Streams .—It is popularly be¬ 
lieved that running water, after a few miles of flow, 
will purify itself to a high degree. As a matter of fact 
the amount of purification that takes place, naturally, 
in a running stream is quite limited, so far as the dis¬ 
appearance of the disease germs is concerned. Their 
dispersion through the mass of the water, and the 
greater dilution caused by the increasing volume of 
flow, are probably the greatest factors in the apparent 
lessening of pollution toward the mouths of rivers. 

Some of the influences tending toward self-purifica¬ 
tion are referred to on page 188. 

Effects of Freezing .—Freezing will not purify or 
render safe for use wa*ter which has previously been 
polluted with fecal matter. Ordinarily it has been ob¬ 
served that clear, transparent ice, when melted, yields 
about ten per cent, as many bacteria as were present 
in the raw water; or, in other words, the percentage of 
removal of the organisms would be comparable to 
that obtained by sedimentation in large reservoirs. 


IN TROD UCTOR Y. 


I 3 




THE PROTECTION OF WATER-SUPPLIES. 

Permissible Pollution .—There are certain conditions 
under which the pollution of a stream is permissible. 
This right is recognized in various States by the Mill 
Acts, which are intended to foster the development of 
industries. These acts could not be operative unless 
the right of stream-pollution were conceded, to a cer¬ 
tain extent. The right to prevent the discharge of 
sewage into a river, when it would result in a public 
nuisance, is now well established. The Supreme 
Court of Connecticut has recently restrained the cities 
of Danbury, Waterbury, and New Britain from dis¬ 
charging their sewage into the Still River, Naugatuck 
River, and Pipers Brook, respectively, because of the 
creation of nuisances. Similar decisions have been 
made in other States. In many cases these decisions 
prepare the way for the collection of damages, the 
cities, or parties causing the nuisances, finding it 
sometimes more convenient to pay the damages an¬ 
nually than to put in the costly works necessary to 
correct the evils. 

Legal Protection of Water-supplies .—The law under 
which New York City maintains the purity of its wa¬ 
ter-supply gives the city power to obtain title to all 
lands in the Croton watershed necessary for the 
construction of dams, reservoirs and appurtenances, 
and also the power to secure title to strips of land 
around the edges of these reservoirs, and the banks of 
the streams feeding them, to insure the sanitary pro- 


14 WA TER FILTRATION WORKS. 

tection of the waiter. A further act, passed in 1893, 
gives the city power to acquire the title to any real 
estate “ for the sanitary protection of all rivers and 
other watercourses, lakes, ponds and reservoirs in 
the counties of Westchester, Dutchess and Putnam, 
so far as the same now are, or hereafter may be, used 
for the supply of water for the City of New York.” 
Unfortunately, as the laws now stand, New York City 
is unable to go to other water sources for an addi¬ 
tional supply, but active measures are being taken to 
remedy this fault so that this great Metropolitan Dis¬ 
trict may have powers similar to those granted to 
other cities of the State. 

In 1898 a law was passed which gives any town in 
New York State the privilege of purchasing the prop¬ 
erty and franchise of its water-works, at any time the 
company may be willing to sell, at a price to be 
agreed upon, the city being empowered to bond 
itself to pay for the works, and also to assume their 
indebtedness and to operate them. 

Provisions for Betterment of Water-supplies .—While 
all these laws regarding the protection of water-sup¬ 
plies have been drawn up with a view of throwing safe¬ 
guards around the public health, the time has come 
when we are forced to realize that legal enactments of 
this kind are inadequate, and that the way must be 
prepared to permit the citizens of any city or town to 
secure water as pure as it is possible to make it. It is 
also true that legislation tending toward that end 
must be secured through the exercise of great discre¬ 
tion and wisdom; any actions that would disturb con- 


IN TROD UCTOR Y. 


15 


fidence in investments, affect the market values of 
stocks and bonds, or raise questions as to the ability 
of concerns already in operation to pay fixed charges 
and customary dividends, would be met with deter¬ 
mined opposition. 

Requirements of Water Companies in the Matter of 
Protection. —The laws of to-day require a water com¬ 
pany to exercise only ordinary and reasonable care in 
the protection of its water; and it has been, thus far, 
impossible to fasten upon a company or corporation 
the responsibility for the deaths of persons resulting 
from the drinking of such water. It is not difficult to 
see why this should be so. In order that the company 
might be forced to pay damages it would have to be 
shown, among other things, that there was an in¬ 
tent to defraud or deceive; that there had been 
criminal negligence in the care of the supply; that 
the water was unquestionably the cause of the ill¬ 
ness or death in question, and that there had not 
been contributory negligence on the part of the 
user. When the pollution of the water is a mat¬ 
ter of common knowledge, fully discussed in pub¬ 
lic and in the press, and when the deceased had 
knowledge of the pollution, it has been held that 
drinking of the water was contributory negligence. 
If the pollution were of an accidental nature the diffi¬ 
culty would lie in proving that the water was the 
cause of the trouble in that specific case, as there are 
many well-known agents, other than water, by means 
of which disease may be spread. 

Protection of Surface Supplies. —Generally speaking, 


1 6 WATER FILTRATION WORKS. 

only those supplies derived from surface gathering 
grounds, small rivers, and, to a certain extent, those 
from ground-water, can be protected by legislative or 
administrative action. As regards protection, large 
rivers are in a different class from small streams. 
Some sanitarians hold that the upland streams should 
be regarded as the water-supply sources of a land, and 
the large streams as its sewers, recommending legis¬ 
lative action to govern the protection of the small 
streams and to determine the degree of permissible 
pollution of the large ones. There are many difficul¬ 
ties in the way of securing uniform legislation on this 
question, because of the great diversity of interests 
affected, and the difficulty of drawing the line be¬ 
tween large and small rivers. The question must be 
specially solved for each locality by the adoption of 
that plan which will be of most benefit to all interests. 
On a very large river, for instance, it would be far 
cheaper, and would afford greater security to the peo¬ 
ple, for all the cities to discharge their sewage into 
the river unpurified, and then purify the drinking- 
water drawn from it, than for them to purify their 
sewage and then drink the untreated river water. 
Under some conditions it might be necessary to 
purify both the sewage and drinking-water. 

The topographical conditions on small highland 
streams are not generally favorable for the develop¬ 
ment of large industries, and it is possible, therefore, 
on such, to enforce restrictions against pollution be¬ 
cause on the small streams the conflicts of interests 
are not so great as on the large lowland rivers. 


IN TROD UCTOR Y. 


i; 


Ownership vs. Legal Protection .—Absolute owner¬ 
ship of the watershed is, by some, considered more 
effective than its protection by legal enactments. 
Manchester and Liverpool own the watersheds from 
which their water is derived, and recently Mr. James 
Mansergh, President of the Institution of Civil En¬ 
gineers, has recommended to Birmingham the pur¬ 
chase of the 45,000 acres of land from which its water- 
supply is drawn. Edinburgh and Glasgow, however, 
protect their watersheds by legal enactments and by 
contracts with the landowners. In this country the 
water companies generally own only the land upon 
which the reservoirs and buildings are situated, ob¬ 
taining easements for right of way for pipe lines, etc., 
and in some of the States depend upon the legal pow¬ 
ers conferred upon the Board of Health to prevent 
the pollution of the water. In some cases these pow¬ 
ers are quite ample, while in others they are practi¬ 
cally inoperative. It is not yet clearly established 
that ownership of the watershed permits of greater 
protection of the water-supply than can be obtained 
by legal enactments without such ownership. Judg¬ 
ing by their typhoid-fever death rates, Manchester 
and Liverpool, owning their watersheds, do not seem 
to be more effectively protected against typhoid 
fever than Brooklyn, New York, Glasgow or Boston, 
having control over their supplies mainly by legal 
powers. 

Effects of Surface Washings .—It is becoming pretty 
well recognized that surface washings are an import¬ 
ant factor in the pollution of water-supplies. It is 


1 8 IVA TER FILTRATION- IVOR ATS. 

quite interesting, in this connection, to note that the 
annual typhoid-fever death rates of New York, Bos¬ 
ton, Cleveland, Detroit, Columbus, Louisville, Pater¬ 
son, Pittsburgh, San Francisco, and Toledo have, at 
various times, fluctuated synchronously for a num¬ 
ber of years with the annual rainfall for the corre¬ 
sponding years; indicating that the typhoid fever in 
these cases was proportional to the amount of pollut¬ 
ing matter washed into their respective sources of 
supply. 

The available evidence goes to show that legal pro¬ 
tection of a water-supply may effect a considerable re¬ 
duction in the death rate of a city, but that such pro¬ 
tection cannot guarantee a water as pure as spring- 
water or properly filtered water. The logical de¬ 
duction is, therefore, that in most cases filtration of 
the water will be required where there is danger of 
sewage-pollution. Of course, as a matter of precau¬ 
tion, all safeguards should be put in force in such mat¬ 
ters, and the direct sewage-pollution of a body of wa¬ 
ter, intended for use as a source of supply, should, if 
possible, always be prohibited, whether or not filtra¬ 
tion is subsequently employed. It is also well estab¬ 
lished that the purification of the sewage of cities, be¬ 
fore discharging it into a stream subsequently used as 
a source of supply, will be less effective as a health 
preservative measure and less feasible from a financial 
point of view than the purification of the drinking-wa¬ 
ter supplies drawn therefrom. Undoubtedly there 
will be many situations where both processes will be 
necessary. 


IN TROD UCTOR Y. 


*9 


It has been the author’s firm conviction for some 
years that the time is not far distant when the public 
will demand the purification of all supplies derived 
from surface gathering-grounds, when practicable. 
A similar view was expressed in the report of the 
Mayor’s Expert Water Commission,* of Philadelphia, 
in reporting upon the Filtration of the Philadelphia 
Supply. 

The available statistics indicate that surface-water 
supplies, except those which have enormous storage 
reservoirs, cannot be generally regarded as safe. 
Large reservoirs afford considerable protection to 
surface-water supplies. The great capacity of the 
reservoirs permits the impurities washed into them 
to be thoroughly dispersed, favors the sedimentation 
of a large percentage of the bacteria, and furnishes 
favorable conditions for the oxidation and absorp¬ 
tion of the nitrogenous matter in the water by 
aquatic plants and microscopic life. 

Large surface supplies are generally more difficult 
to protect than small ones. The actual protective 
measures are naturally divided into two classes: those 
which must be used when the works are building, 
and those which must be enforced after the works are 
placed in operation. When a supply of surface-water 
is to be furnished, it is first necessary to acquire the 
land upon which the reservoirs will be situated. In 
large works this will require the acquisition of many 


* Report on the Extension and Improvement of the Water- 
supply of the City of Philadelphia, by Rudolph Hering, Joseph M. 
Wilson, Samuel M. Gray. 



20 


WA TER FILTRATION WORKS. 


farms, and perhaps villages and towns, and the de¬ 
struction of many industries. The land taken should 
include everything lower than high-water line of the 
proposed reservoir, with an allowance of two or three 
feet for exigencies; in addition, a strip, 200 or 300 
feet wide, should be secured all around the water, to 
give perfect control over the shores. The same policy 
should be followed, if possible, in regard to the prin¬ 
cipal feeders of the reservoirs. This property is se¬ 
cured usually by appraisal by commissioners, and in 
many cases it results in a direct benefit to the inhabi¬ 
tants of the territory taken. 

After the site has been acquired, the fences and 
buildings must be removed to other sites, or burned, 
and the vegetation must be cut down and burned, or 
removed. The necessity of removing the top soil and 
small vegetation has in late years been given much 
prominence. Some of the older Boston reservoirs 
were not so treated, and the great deterioration of the 
water due to the slowly decomposing organic matter 
was a source of much anxiety. This trouble has been 
remedied at great expense by drawing down the wa¬ 
ter, pulling out the stumps, removing the soil, in some 
cases to great depths,' and paving the slopes. Late 
investigations have shown that the removal of from 
6 to 12 inches of the top soil will accomplish all that 
can be desired, and the covering of the mucky places 
with a foot of gravel has served as well as remov¬ 
ing the entire deposit. It is also necessary that 
the bottom of the reservoir should be graded so 
that all the water will drain to the outlet, and not 


IN TROD UCTOR Y. 


21 


leave stagnant, isolated pools when the water is 
drawn down. In addition to the treatment of the 
reservoir site, it is necessary to drain, or cut off, 
the swampy areas on the watershed by ditches or 
banks. Sometimes a few ditches satisfy the condi¬ 
tions, and sometimes it is necessary to convey 
the water feeding the swamp in direct channels to a 
near-by watercourse, and isolate the swamp by em¬ 
bankments. While all these operations are going on, 
and while the dams and accessory works are build¬ 
ing, tight portable earth-closets must be provided 
for the use of the workmen and every precaution 
must be taken to insist upon their proper use and care, 
there being several cases on record where epidem¬ 
ics have resulted from the neglect of this simple pre¬ 
caution. 

During the operation of the works the principal 
sources of pollution that must be controlled are the 
washings from the streets and roads; the washings 
from the fields; the pollution from swamps and bogs; 
the refuse from manufacturing establishments; sew¬ 
age matter; garbage; farm refuse, and the drainage 
from cemeteries. 

Much of the pollution from the street-washings, in 
the villages, can be abated by efficient street-cleaning 
methods and sanitary regulations regarding the col¬ 
lection and disposal of the refuse. Street-sweepings 
have a value and can readily be disposed of to farm¬ 
ers, in the neighborhood, for fertilizing purposes. 
The washings from rural roads can nearly always be 
purified, to a certain extent, by diverting the ditch- 


22 


WATER FILTRATION WORKS. 


water at intervals over lands adjoining- the road, 
whereby, through sedimentation, straining and par¬ 
tial filtration, a large amount of the objectionable im¬ 
purities may be removed. The washings from culti¬ 
vated lands, when the fertilizer is of an objectionable 
character, should be spread out over grass land, or 
passed through a porous soil, for a considerable dis¬ 
tance, before being allowed to flow into the feeders 
of the supply. 

Protection from Sewage-pollution .—The problem of 
dealing with the sewage of the villages resolves itself 
generally either into a system of dry removal, or into 
a system of water carriage, followed by purification, 
before allowing it to flow into the feeders of the sup- 
ply. 

The most convenient method for dry removal is to 
provide the closets with coverable pails or boxes, into 
which dry earth or ashes may be thrown, as an ab¬ 
sorbent. This method has been in use at Hemlock 
Lake, N. Y., the source of the domestic supply of 
Rochester, since 1885, and has proven satisfactory. 
It has the advantage that the matter deposited in the 
receptacles can be kept from direct contact with the 
air, and hence, also, away from flies. Pail contents, 
garbage, and other decomposable matter should be 
buried in a safe place, or burned in refuse destructors. 
Human faeces should not be exposed on the surface of 
the ground near a water-supply source nor used for 
fertilizing the soil. 

The principal disadvantages of the pail system when 
applied to cities are the great cost and inconvenience 


INTROD UCTOR Y. 23 

of the method as compared with the water-carriage 
system followed by the purification of the sewage. 

The State Boards of Health generally enact laws to 
prevent the discharge of sewage from cities into the 
water-supply sources of other cities, and therefore, 
upon proper complaint, such nuisances may be 
abated. Boston, as is well known, encourages the 
towns and cities within the shed of her water-supply 
to take their sewage outside the limits, if possible, or 
to put in satisfactory plants for purification of the 
same, paying fifty per cent, of the cost of the work, 
the towns paying the other fifty per cent. The great¬ 
est difficulty is generally in enforcing the law, as this 
can only be done by proper legal processes, entailing 
often considerable delays. 

Protection of Lake Supplies .—The protection of sup¬ 
plies derived from large lakes is hampered by many 
difficulties, and the protective measures must depend 
upon the direction of the surface and submerged cur¬ 
rents, the size and growth of the city, the relative lo¬ 
cations of the outlets of sewers, drains and large pol¬ 
luted streams, the amount and direction of the lake 
traffic, the depth of the water, annual rainfall, and 
many other factors. An interesting case of the pollu¬ 
tion of a lake supply has been reported by Professor 
Gardiner S. Williams, formerly Engineer of the Board 
of Water Commissioners of Detroit, Mich. The sew¬ 
age of Port Huron is discharged into the Black River, 
a sluggish stream emptying into Lake St. Clair, 60 
miles above Detroit. In 1891 the Government com¬ 
menced dredging operations in the Black River to 


24 


WATER FILTRATION WORKS. 


improve navigation, and the mud taken from the bot¬ 
tom was dumped into the St. Clair River, about 60 
miles above the intake of the Detroit water-works, 
which are just below Lake St. Clair. Fifty days after 
the dumping of the first scow-load of polluting mate¬ 
rial from the Port Huron sewers into the S ; t. Clair 
River, there were four deaths from typhoid fever in 
Detroit. This would allow ten days for the water to 
flow from Port Huron to the intakes, fourteen days 
for the disease to incubate, and about twenty-six days 
for the disease to run its course. Many cases followed 
these four, the disease disappearing some weeks after 
dredging operations were suspended. The next year 
typhoid appeared again after the dredging had begun; 
and again it disappeared when dredging was stopped. 

These conditions have followed one another since 
that time, and investigations have shown that they 
prevailed in previous years. As far back as 1886 it 
was found that typhoid fever appeared in Detroit dur¬ 
ing those years when dredging operations disturbed 
the bottom of the St. Clair River or Lake St. Clair, 
above the intake of the water-works. 

All lake cities, as they grow to larger proportions, 
find it necessary to gradually extend their intakes 
further from the shores, unless the purification of the 
water is determined upon. At the city of Chicago the 
intake has been pushed out successively from 700 feet 
to two miles and then to four miles. Cleveland has 
now under construction a new intake tunnel which 
will be 26,000 feet long, when completed; and the in¬ 
take for the city of Buffalo has been extended from 


INTROD UCTOR Y. 


25 


330 feet to 1,020 feet. In Zurich, Switzerland, instead 
of extending the intake further from the shore to get 
pure water, a large plant has been constructed for 
filtering the entire supply from the lake. 

THE PURIFICATION OF WATER BY FILTRATION. 

In the following pages the works and operations 
necessary for the purification of drinking-water for 
cities and towns and large institutions, by filtration, 
will be described with some fulness. The science of 
water-purification is still in process of development. 
Each new experimental plant brings to light new dif¬ 
ficulties and new methods of overcoming them. Ex¬ 
perimental work, such as that done at Louisville, Cin¬ 
cinnati, Pittsburg, Providence, and Philadelphia, and 
now under way at New Orleans, is of incalculable 
value, as it leads to the discovery of the proper treat¬ 
ment for the purification of waters of different kinds. 
Processes that are applicable for the treatment of clear 
polluted waters fail entirely with turbid waters; and 
turbid waters themselves vary so greatly in regard to 
character and seasonal distribution of sediment that 
each case requires a special study. Some clear wa¬ 
ters, also, on account of rank algae growths, at cer¬ 
tain seasons, must have special treatment before they 
can be filtered successfully. 

The filters described at length in this work are 
classified under two heads—slow sand-filters and 
rapid sand-filters. These terms must be used in the 
restricted sense; both refer to filters in which the 


26 


WATER FILTRATION WORKS. 


filtering medium is sand. The slow sand-filters may 
be, though they generally are not, operated with the 
aid of chemicals for producing the surface film, while 
the rapid sand-filters can only be efficient by using a 
coagulant, such as aluminum hydrate, to form the 
film artificially and rapidly. 

Other types, such as the Fischer or Worms filter, 
using slabs of concrete, and the Pasteur-Chamber- 
land, using tubes of unglazed porcelain, belong in a 
different class. 

There are also slow sand-filters operated in con¬ 
nection with a coagulant; such as the filters at 
Antwerp, where the coagulant is ferric hydrate, pro¬ 
duced by the Anderson process, and the experimental 
filters tested at Cincinnati by Mr. Fuller, and called 
by him “ Modified English Filters.” There is also the 
process used in the Maignen system, in which a layer 
of asbestos forms the surface film over the sand. 

The indications are that the development of some 
preliminary process for straining out the finely di¬ 
vided particles of clay, by the use of prepared sponges, 
layers of cloth, or other absorbent materials, instead 
of using a coagulant, may, in the future, play an im¬ 
portant part in water-purification. 

As a rule, most waters which would be used for a 
water-supply require the same cycle 1 of operations to 
render them fit for use as drinking-water; that is, the 
removal of turbidity, color, and pathogenic bacteria. 
These operations usually require works for removing 
the suspended matter by sedimentation, with or with¬ 
out the coagulation of the liner particles; the removal 


INTROD UCTOR Y. 


2 7 


of color and pathogenic bacteria by filters, with or 
without the aid of coagulation, and the storage of the 
filtered water in sufficient quantities to permit the 
filters to operate at a nearly uniform speed, although 
the draft on the works may vary considerably in rate 
at different times of 'the day. These different works 
will therefore be discussed in the subsequent pages in 
the following order: 

Intakes. 

Sedimentation. 

Settling basins. 

The purification of water by slow sand-filtration. 

The design, construction and operation of slow 
sand-filters. 

The purification of water by rapid sand-filtration. 

The construction and operation of rapid sand-filters. 

Other methods of filtration. 

Filtered-water reservoirs. 


CHAPTER II. 


INTAKES, SEDIMENTATION, AND SETTLING 

BASINS. 

INTAKES. 

Flowing waters may be divided into two general 
classes: those in which tidal influences may cause a 
reversal of current, or at least a checking of velocity, 
and those in which the flow is continuous in one di¬ 
rection. 

Tidal Streams. —Water-supplies taken from streams 
subjected to tidal reversals of current are usually also 
sewage-polluted, and, therefore, in the location of the 
intake due regard must be had to the time of collec¬ 
tion of the water to insure that it may be taken only 
when it is at its best. The intake for the Antwerp 
works is at Waelhem, a small village about eight miles 
to the south, on the banks of the River Nethe. About 
two miles above Waelhem the Nethe is joined by two 
streams, the Seine, upon which Brussels is situated, 
and the Dyle, flowing through Malmes. Below the 
junction the river is called the Rupel; this flows into 
the Scheldt, upon which Antwerp is situated. The 
range of tide at Waelhem is about 13 feet 6 inches. In 

order to avoid taking in the polluted waters of the 

28 


INTAKES. 


29 


Rupel, as they flow past Waelhem, on the flood tide, 
and the waters of the Nethe, contaminated at low 
water with the sewage of the towns situated above the 
intake, the water is let into the settling basins three 
hours after high water. The bottom of the intake is 
.33 foot above low tide. Water taken under these 
conditions and purified by ordinary sand-filtration 
was pronounced by the authorities sufficiently good 
for the supply of the city. At Shanghai the water is 
taken from the River Huang Poo, a branch of the 
great Yang-tse-Kiang. The range of the spring 
tides is from 8 to 9 feet. The intake for the water¬ 
works is located below the city of Shanghai, where the 
great dilution from the Yang-tse-Kiang, on flood 
tide, and the wide section of the river, make the dan¬ 
ger from pollution less than if the intake were above 
the city, where the river section is very much smaller. 
The valves of the intakes are placed two feet above 
the low-water level, so that no water can enter them 
until fully one hour after flood tide has set in. By this 
means the sewage of the city and its suburbs is washed 
into the upper reaches of the river during the time the 
water is being taken into the settling basins. What¬ 
ever sewage matter may have gone down the river on 
the previous tide is so greatly dispersed in the waters 
of the Yang-tse-Kiang that it is hardly detectable. 

Rivers with Stable Banks above Flood Height, and 
with small Range of Fluctuation of Level. —If a river 
has stable banks, at a slight elevation above high 
water, a fair velocity, with a small range of fluctuation 
of surface elevation, the intake should be constructed 


30 


WA TER FILTRATION WORKS . 


with the bottom low enough to collect the water at all 
times, and should consist of one or more pipes or con¬ 
duits ending in a chamber at the face of the bank. 
The distribution of sediment in rivers, both in the ver¬ 
tical and horizontal, is discussed on pages 35 and 36. 
Movable duplicate screens in the chamber will pre¬ 
vent the entrance of floating and other objects that 
might interfere with the valves of the pumps. At 
Berlin, at the Mueggle See works, on account of the 
shallow water and sloping bottom, the water near the 
shore is generally muddy from the action of the 
waves. To secure clearer water the bottom of the 
lake was dredged to a depth of 6.6 feet in front of the 
works, for a distance of about 400 feet from the shore 
to the point where the bottom drops off rapidly to a 
depth of about 26 feet. The intakes are box con¬ 
duits, with a sectional area of about 24 square feet 
each, built up of oak planks, and extending from the 
deep water to the screen wells or shafts at the shore. 

Rivers with Stable Banks below Flood Height .—If the 
river has stable banks, which are below flood height, 
and the works are protected by levees and dikes, the 
intake may still be as above described, but it will then 
be necessary to provide a gate in the conduit, placed 
in a manhole located in the dike, in order to regulate 
the amount of water admitted to the works when the 
river is very high, as was done at Hamburg. If the 
gate were located behind the dike the hydrostatic 
pressure on the inside of the conduit might cause its 
rupture if it were of masonry construction. 

If the settling basins are lower than the river, in ad- 







































SEDIMENTA T10N. 


33 


dition to the gate in the conduit in the dike, referred 
to above, it may sometimes be necessary to provide a 
reflex gate or valve to prevent the water from escap¬ 
ing to the river, in case the attendants should neglect 
to close the gate when the basins were filled. If the 
basins are to be arranged to be flooded quickly when 
the water is at its best, a relief pipe must be built to 
provide means for the escape of the air contained in 
the conduit, thus avoiding the dangers incident to 
concussion, as was done at Antwerp. 

Rivers with Shifting Banks and Bottoms, and Great 
Fluctuation of Level. —When the river has shifting 
banks and bottom, and the range of fluctuation of 
surface level is great, intakes become very expensive 
structures. The intake, in this case, must start from 
a point in the bed of the stream where the chan¬ 
nel is permanent, and should consist of a masonry or 
other heavy structure, resting on a firm foundation, 
and constructed with a view of resisting the action of 
the water, ice and floating objects. Under these 
conditions pumping must always be resorted to be¬ 
tween the river and the settling basins. The conduit 
from the intake to the pump-well must pass under 
the bed of the river, and may be enlarged, before 
reaching the pumps, to form the screening chamber. 
The intake at the St. Louis water-works is of this 
type. 

SEDIMENTATION. 

Amount, Character and Distribution of Sediment .— 
The purification of polluted water may require the 


34 


IVA TER FILTRATION WORKS. 


removal therefrom of suspended particles of finite di¬ 
mensions, matters in solution, and microscopic ob¬ 
jects, both animate and inanimate. For the removal 
of the first class of matter, straining, or sedimentation 
alone, or combinations of these methods, will gener¬ 
ally suffice; for the second and third classes, chemical 
or mechanical treatment, or some method of filtra¬ 
tion, will probably be necessary. 

Waters taken from large lowland rivers flowing 
through valleys or plains, formed of the detritus and 
washings of the highlands, carry, at all seasons, large 
quantities of matter in suspension. A certain part 
of this matter can be removed by allowing the water 
to stand in comparative quiescence in large settling 
basins or reservoirs. The amount of matter that can 
be carried in suspension depends on the viscoscity of 
the water; the chemical composition and degree of 
comminution of the matter in suspension; the eddies 
caused by the deflection of the strata of water by im¬ 
pingement against the bottom and sides of the 
stream; vortex motion, and probably on other imper¬ 
fectly understood causes. It will be seen therefore 
that a river may carry different amounts of matter in 
suspension at different periods of the year, and at dif¬ 
ferent portions of its course. This is well illustrated 
in the case of the Mississippi River and its tributaries, 
the estimated average turbidity in parts per million 
of the Allegheny at Pittsburgh being given as 50; 
the Ohio at Cincinnati as 230; the Ohio at Louisville 
as 350, and the Mississippi at New Orleans as 
560. The average estimated turbidity of the Merri- 


SEDIMENT A TION. 


35 


mac at Lawrence is given as io; of the Hudson at 
Albany as 15 and the Potomac at Washington as 80 
parts per million respectively.* The quantity of sedi¬ 
ment carried in flowing waters is discussed more at 
length on pp. 64 et seq. In large rivers, flowing 
through lowlands, it has been frequently observed 
that the amount of suspended matter gradually de¬ 
creases, per unit of volume of water, toward the em¬ 
bouchure, though this may not always be the case. 
It has also been observed that the weight of sediment 
per unit of volume of water does not always increase 
with the velocity of the river, nor with the volume of 
flow, but that a greater load is often carried per unit 
of volume in dry-weather flows than during floods. 
In turbid flowing water, that near the surface contains 
the least suspended matter per unit of volume of wa¬ 
ter. It is also apt to be more free from bacteria, both 
on account of the influence of sunlight, and from their 
being carried down by sediment. That the amount 
of sediment is less at the surface than at other depths 
is shown by numerous recorded observations. It is 
perfectly shown by the determinations for the 
Garonne,f and also in the data compiled by Elon 
H. Hooker, Ph.D., C.E.J 

Such few measurements as have been made throw 
no light on the question as to whether more sediment 

* Report to Hon. James McMillan, Chairman Senate Com. on 
the Dist. of Columbia, Washington, D. C., by Rudolph Hering, 
George W. Fuller, and Allen Hazen. 

f Notice sur le Port de Bordeaux, M. R. de Volontat, Paris, 
1886. 

J Trans. Am. Soc. C. E., vol. xxil. p. 414. 



36 WATER FILTRATION WORIIS. 

is to be expected in the centre of the stream than 
near the banks.* So far as our present knowledge 
goes there seems to be but little difference. 

There is a certain degree of comminution, for any 
given material, at which the rate of sedimentation of 
its particles in quiet water would be so slow as to be 
practically zero. This partly explains why water 
which contains very finely divided sediment clears 
slowly, and also why, after a certain period of time, 
practically the same amount of clarification will exist 
from the top to the bottom of the water. This occurs 
in the case of the water of the Mississippi at St. Louis. 
There it has been found that water can be drawn 
off from the settling basins at the thirteen-foot level 
with the same benefits, as to clarification, as could be 
had by drawing it off from the top. 

Turbidity. Standard of Measurement .—The method 
devised by Mr. Hazen for the measurement of tur¬ 
bidity is based on the depth, in inches, that a plati¬ 
num wire i mm. in diameter and i inch long can be 
seen when submerged below the surface, the results 
being expressed in the reciprocals of these depths. 
Thus, at a depth of i inch the turbidity is i, 
at 4 inches it is .25 and at 40 inches .025, etc. 
The limit of permissible turbidity is variously esti¬ 
mated at from .2 to .025, as water of this degree 
of clearness will show no color to the ordinary ob¬ 
server when seen through a glass. The permissible 
limit, however, must depend largely on the people 
who use the water, and turbidity much higher than 


* Report on the Mississippi. Humphreys & Abbott, 1861. 






SED1MENTA TION. 37 

this, occurring only occasionally, might not cause 
unfavorable comment. 

Another means of indicating the turbidity of a wa¬ 
ter is to state the parts per million of suspended mat¬ 
ter contained therein. This method was adopted by 
Mr. Fuller in his Louisville and Cincinnati experi¬ 
ments. Mr. Geo. C. Whipple, Director of the Mt. 
Prospect Laboratory, Brooklyn, uses silica stand¬ 
ards,* prepared from diatomaceous earth and distilled 
water for estimating turbidity. Tubes are filled with 
the mixture diluted by known quantities of distilled 
water, and the sample under observation is compared 
with the various standards to determine its turbidity. 

Rate of Sedimentation .—The rate at which clarifica¬ 
tion takes place in a quiescent turbid water varies ac¬ 
cording to many different causes. In 1865 Mr. Flad 
found, from experiments with water taken from the 
Mississippi at St. Louis,f that of a total of 1,000 parts 
in suspension, 944.5 parts settled during the first 24 
hours, 22.35 parts during the second 24 hours, 2.92 
parts during the second 48 hours, while 30.23 parts 
were still in suspension after 96 hours. 

Water taken from the Garonne often shows tur¬ 
bidity after eight days, and muddy water taken from 
the lower Elbe shows very slight sedimentation until 
after the lapse of 24 hours. The water of the Missouri, 


* Silica Standards for the Determination of Turbidity in Water. 
Geo. C. Whipple and Daniel D. Jackson. Technology Quarterly, 
Dec , 189Q. 

f Silt Movement in the Mississippi. R. E. McMath, Van A T os- 
trand's Mag., 1883. 





38 .WATER FILTRATION WORKS. 

at Omaha, often refuses to settle in a period of 72 
hours, while the waters of the Delaware and Schuyl- 



PERIOD OF QUIESCENT SUBSIDENCE 
HOURS 


Fig. i.—Rate of Subsidence of Mississippi River Water at 

St. Louis, Mo. 

kill Rivers, at Philadelphia, sometimes show more 
matter deposited in a given sample of water at the 
end of 24 hours than in the same sample after the 
lapse of 48 hours. 

The rate of clarification of the Mississippi River 
water, as determined by the experiments of Mr. Flad, 






















SEDIMENTA TION. 


39 


in 1886, is shown in Fig 1, on page 38. The curves 
represent the rate of deposition of sediment in differ¬ 
ent periods of time for two sets of experiments. It 
will be observed that the amount of sedimentation 
which took place after the first 24 hours was very in¬ 
significant. The water in experiment II cleared more 
slowly than in experiment I, indicating a more finely 
comminuted sediment. 

At Cincinnati* the Ohio River contains, at times, 
a sediment so finely divided that only 75 per cent, of 
it, on the average, can be deposited in three days by 
simple subsidence. The relative estimated range of 
removal of suspended matters, in different periods of 
time, are given as follows: 


table v. 


Period of Subsidence. 

Percentage Removal of Suspended Matter. 

Maximum. 

Minimum. 

Average. 

24 hours. 

85 

25 

62 

48 “ . 

90 

30 

68 

72 “ . 

95 

40 

72 

96 “ . 

95 

45 

76 


Effects of Winds .—Experiments made at St. Louis, 
to show the relative rates of subsidence of the water 
in the settling basins open to the weather, and in a 
stand-pipe protected from the wind, demonstrated 
that there was no practical difference between the 


* Purification of the Ohio River Water, for the Improved Water- 
supply of the City of Cincinnati, O., 1899. 

















40 


WATER FILTRATION WORKS. 


two. The samples from the stand-pipe were taken 
six feet below the surface, and those from the settling 
basins were taken from the surface of the water. On 
the strength of these indications it was decided not to 
cover any settling basins needed in future extensions 
of the works. 

Effect of Temperature .—The influence of temper¬ 
ature on the rate of sedimentation has been found to 
be undoubted and positive; sedimentation taking 
place more rapidly in warm* than in cold water.f 
A difference in temperature of a few degrees in the 
water in different parts of the settling basin may act 
as a disturbing element to prevent sedimentation by 
setting up convection currents due to differences in 
density. At St. Louis, in the Chain of Rocks settling 
basins, vortex motion has been observed four days 
after filling has been stopped .% 

Effect of Light .—Light is also a factor in the rate of 
sedimentation, though its effects may be too slight to 
entitle it to mention. Mr. Andrew Brown, in experi¬ 
ments with phials filled with turbid water, found that 
there was a tendency toward more rapid settling in 
those protected from light than in those not so pro¬ 
tected. Not enough is yet known about this subject, 
however, to enable us to say whether the phenomena 
should influence in any way the designing of settling 
basins. 


* Subsidence of Fine Solid Particles in Liquids: Carl Barus, 
Bulletin No. 36 U. S. Geological Survey, 1886. 
f Mass. State Board of Health, 1895, H. W. Clark. 

X Sedimentation. James A. Seddon, Eng. News , Dec,, 28, 1889. 



SEDI MEN TA TION. 4 ! 

Use of Chemicals to Aid Sedimentation .—The use of 
chemicals for hastening sedimentation may some¬ 
times be advisable if the water contains in suspension 
particles of argillaceous, silicious or earthy matter, so 
finely divided that their removal cannot be accom¬ 
plished by simple sedimentation. 

Such a plan has been recommended for Cincin¬ 
nati, where it will be most advantageous to intro¬ 
duce the sulphate of alumina into the water as it 
enters the settling basins, securing in a few hours 
as much clarification as could be had by several days 
of simple subsidence. A similar practice has been 
recently recommended for the City of Washington, 
D. C.* At Sandhurst, Victoria, Australia, the water 
from surface gathering grounds contained as much 
as from 24 to 32 grains of yellowish-brown clayey 
matter per gallon, and filters were not able to remove 
it. The addition of 5.6 grains of lime per gallon gave a 
clear water after 10 hours of settlement. 

Results of Sedimentation .—As a general thing, prac¬ 
tically all the suspended matter which can be econom¬ 
ically removed by simple subsidence will be precipi¬ 
tated in 24 hours, although in some cases longer set¬ 
tlement may be more economical than coagulation 
and secondary subsidence. Frequently when certain 
waters stand in reservoirs exposed to the bright sun¬ 
light, they develop very disagreeable odors and 
tastes, the removal of which requires a further puri¬ 
fying treatment. Such troubles add considerably to 

* Purification of the Washington Water-supply, Senate Report 
2380. 56th Cong., 2d session. 



42 WATER FILTRATION WO RETS. 

the expense of purification, necessitating, in some 
cases, thorough aeration; in others filtration and 
aeration, and in others some chemical or mechanical 
treatment to remove the objectionable qualities. Too 
great a storage capacity, therefore, may sometimes 
prove a source of expense, and in such cases it may be 
found cheaper to remove only a part of the suspended 
matter by means of settling basins, and to depend 
upon coagulation and secondary subsidence, or upon 
filters operated at a comparatively high rate, with a 
coagulant, for the removal of the remainder. 

The results that usually may be expected, toward 
effecting purification by sedimentation, are the re¬ 
moval under poor conditions of from 25 to 50 per 
cent., and under favorable conditions of from 90 to 99 
per cent, of the suspended matter by weight. With 
the deposition of the sediment, there will also take 
place, to a considerable extent, a subsidence of some 
of the bacteria in the water. Examinations made by 
Frankland showed that from 80 to 90 per cent, of the 
bacteria may be removed in this way, and experiments 
made by Prof. C. C. Brown, in the St. Louis settling 
basins, show a quite decided reduction in the number 
of bacteria after 24 hours of settlement. 

Efficiency of Sedimentation .—The relative economy 
and efficiency of the continuous and intermittent 
methods of operating settling basins are somewhat 
disputed points in this country. The practice in Eu¬ 
rope inclines toward continuous operation. In 1886 
certain experiments on this subject were conducted 
in St. Louis, under the direction of the Water Com- 


SEDIMENTA ETON. 


43 


missioner, Mr. M. L. Holman. At the time of these 
experiments there were in operation four settling 
basins at the Chain of Rocks Station, each 600 feet 
long, 270 feet wide and 13 feet deep. They were oper¬ 
ated on the fill-and-draw method, one in filling, one 
in drawing and two in settlement. The average 
quantity drawn off at each drawing was from 10 to 12 
million gallons. The daily average consumption was 
about 32 million gallons. Thus each basin had an 
average period of rest of from 16 to 18 hours, includ¬ 
ing the time of filling and drawing. The clarified wa¬ 
ter went to a well called the “ clear well,” from which 
it was drawn into the distribution system. The ex¬ 
periments on continuous flow were made with a flume 
2\ feet deep, 4^ feet wide and about 500 feet long. 
The raw water taken to the flume was the same as was 
taken into the basins, and in the diagram is called the 
“ Distributing Well.” The relative clarification was 
determined by an apparatus called a comparator, 
which served to show the depth of the sample of wa¬ 
ter which would obscure diffused daylight, and thus 
indicate the degree of clarification. Its determina¬ 
tions while not exact, and subject to a considerable 
personal factor, serve as a fair guide in judging of the 
results obtained. These data are plotted in Fig. 2. 

In this diagram is shown the degree of clarification 
in the different portions of the flume, as the water 
passed through it at different mean velocities. The 
figures on the right are the comparator readings; the 
higher the number, the clearer the water. The in¬ 
clination of each line then represents the rate of clear- 


44 


WA TER FILTRATION WORKS. 



Fig. 2.— Rate of Clarification of Mississippi River Water 
at St. Louis, Mo., in Passing Slowly Through a Long 

Flume. 













































SETTLING BASINS. 


45 


ing. The diagram shows that the greater the velocity 
of flow, the less rapid the clearing, and the less abso¬ 
lute clearing accomplished; and the slower the veloc¬ 
ity the more rapid the clearing and the more absolute 
clarification accomplished in traversing the flume; 
and also that probably the effect of the dams across 
the flume was detrimental to the settlement in every 
case. The detrimental effect was more evident at the 
higher velocities. At the slow velocities of 1.3 and 1.4 
inches per minute the efficiency of the continuous 
flow, even in this small flume, was about the same as 
resulted from 16 to 18 hours of quiet settlement in the 
large settling basins. It is probable that a velocity of 
2.4 to 2.5 inches per minute would, allowance being 
made for the bad effect of the dams, effect a clarifica¬ 
tion practically equal to that obtained by from 16 to 
18 hours of quiescent settlement, in traversing the 
500 feet of flume. It is also probable that this effect 
might have been looked for with a length of flume of 
about 400 feet if the dams had been omitted. 

SETTLING BASINS. 

Designing. 

Location .—Settling basins are sometimes placed so 
low that the water from the river may be flooded into 
them rapidly by gravity. They are frequently placed 
on the bank, and are filled by pumping, and they are 
also sometimes placed on a hill, the water being 
pumped into them, and, after clarification, allowed to 
flow into the distribution system. In Antwerp and 


46 


WATER FILTRATION WORKS. 


Rotterdam, situated on the tidal rivers Nethe and 
Maas respectively, the quality of the raw water varies 
with the tides, and the settling basins have been 
placed sufficiently low to permit of a whole day’s sup¬ 
ply being rapidly flooded into them when the water is 
in its best condition, without pumping. In several of 
the London works also the settling basins are lower 
than the rivers. In most of the German works, how¬ 
ever, and in many of the English, the basins are high 
enough to be above floods and the raw water is 
pumped into them. At Altona the raw water of the 
Elbe is pumped into the basins on a high hill, flows to 
the filters by gravity, and thence to the city. Similar 
arrangements will also be necessary in some of the 
filter plants now being built for the city of Phila¬ 
delphia. 

Capacity .—The capacity which should be given to 
the settling basins will depend upon the purpose they 
are intended to serve, and will vary from ^ or -J of a 
day’s supply of water to several days’ supply. If the 
river from which the supply is drawn is only slightly 
turbid, ordinarily, but is subject to being made roily 
for three or four days at a time, by floods of short du¬ 
ration, a small capacity only need be provided. If the 
river is constantly turbid, and carries a great or even 
greater proportion of matter in suspension during 
dry-weather flow than during floods, like the lower 
Mississippi, and portions of the Red, Arkansas and 
Missouri Rivers, a storage capacity equal to at least 
one or two days’ supply should be provided, and very 
frequently chemicals will have to be employed to 


SETTLING BASINS . 47 

bring about a secondary subsidence of the finer parti¬ 
cles. 

It sometimes happens, however, that it is desirable 
to have a large storage capacity for other consider¬ 
ations than those of economy of operation. The city 
of London offers an example of such conditions. The 
valleys of the rivers Thames and Lea, above London, 
are quite thickly populated, and the sewage of this 
population finds its way into the streams, after hav¬ 
ing been treated chemically, or by its application to 
land; the treatment is thoroughly carried out, how¬ 
ever, only in times of low water. When the rivers are 
high, a large amount of untreated sewage goes into 
them, through storm-water overflows, and by di¬ 
rect discharge. The water companies, in order to 
secure the water in as good a condition as possible, 
pump it from the river to the settling basins only 
when the rivers are low, and therefore provide suffi¬ 
cient storage capacity to carry them over periods of 
high water. This has resulted in the construction of 
basins very much larger than would otherwise have 
been necessary; the different companies now having 
storage capacity ranging from about two to fourteen 
times their daily average consumption, with a tend¬ 
ency to still further increase the reserve quantity. 

Depth .—Before determining the area required for 
settling basins it is necessary to decide upon their 
proper depth. To establish this point it will be neces¬ 
sary in some cases to make experiments, because 
the deeper it is possible to make the basins the 
less area will be required. Usually it will be found 


48 WATER FILTRATION WORKS. 

that the depth can be so great that the problem be¬ 
comes one of economically designing a storage reser¬ 
voir to hold the given amount of water. This was 
found to be the case at St. Louis. In practice the 
depth of water is usually made from ten to sixteen 
feet, allowing from two to three feet of this depth for 
the accumulation of sediment. Since in small basins 
the proportionate cost of the walls around the 
periphery is greater than in large ones, it is evident 
that it would be economy to make small basins shal¬ 
low and large ones deep. A less depth than about ten 
feet, however, would scarcely be recommended. 

Length, and Velocity of Flow .—In basins to be oper¬ 
ated on the continuous-flow method the first point to 
be decided is the proper velocity to be given the wa¬ 
ter in its passage through the basins. 

If the flow is too rapid, eddies will be produced 
which will interfere with the subsidence of the finer 
matter. It would obviously be poor economy to con¬ 
struct very long basins for a water which clears rap¬ 
idly, because most of the sedimentation would take 
pLce near the inlet for raw water, and the surplus 
length would be unnecessary. In a water which 
clears very slowly, however, that is, water dis- 
coiored largely with clay or very finely comminuted 
matter, better results should be obtained by making 
the basins long in order to give sufficient time for 
sedimentation. 

As to the maximum allowable velocity, author¬ 
ities differ. Where the process is to be followed 
by coagulation or filtration, greater absolute ve- 


SETTLING BASINS. 


49 


locities are sometimes allowable than where sedi¬ 
mentation is the only treatment. Sedimentation 
alone cannot be relied on to produce sufficient clari¬ 
fication excepting in waters which ordinarily run clear 
enough for use without it. If the normal condition of 
the water is turbid, there is almost always a perma¬ 
nent discoloration due to clay and finely divided or¬ 
ganic matter in suspension, which simple sedimenta¬ 
tion alone would not remove in many days of absolute 
rest. We find, therefore, in the works which have 
been executed, that the assumed velocity varies very 
greatly, according to the judgment of the different 
designers. In Hamburg and Altona, which use the 
turbid, dark-colored water of the Elbe, the velocities 
are about 4.5 and 3.8 inches per minute respectively. 
At both of these places the water is subsequently fil¬ 
tered. Professor Freuhling* recommends a velocity 
of from about 2.35 to 4.7 inches per minute. 

The data for the settling basins at several places are 
given in Table VI. 

Having decided upon the capacity and the rates of 
flow through the basins, their lengths may be found. 
In large works the determination of the number of 
basins and the width of each is a matter of economi¬ 
cally subdividing the total capacity (knowing their 
depth, and length, and the approximate amount of 
sediment to be removed in a given time) in such a 
manner as to leave a sufficient number of basins al¬ 
ways in operation while one is being cleaned or re¬ 
paired. The number of basins to be provided in a se- 


* Handbuch der Ingenieurwissenschaften. 




5 ° 


WA TER FILTRATION WORKS. 


ries designed for the fill-and-draw method should be 
such as will give the longest period of rest to the 
standing water, regard being had to the relative 
economy of construction of different designs; for it 
must be borne in mind that the interest and sinking- 
fund charges are a large part of the cost of sedimen¬ 
tation, being nearly always more than the cost of 
operating and cleaning the basins. 

TABLE VI. 


City. 

Daily 

Consumption. 

Capacity of 
Basins. 
Gallons. 

No. of Basins. 

Approximate 
Days 1 Storage. 

Daily Delivery, 

Gals, per sq. ft. 

of Effective 

Area. 

Velocity of Flow 

in Basin. Ins. 

per Minute. 

Antwerp. 

2,310,000 

1,320,000 

2 

I 

1277 

1-75 

Shanghai. 

3,000,000 

6,130,312 

2 

2 

1250 

•93 

Baroda. 

3,000,000 

16,700,000 

2 

5-6 

545 

•35 

Hamburg. 

35,000,000 

84,000,000 

4 

2.4 

3673 

4-56 

Prof. Frueh- 







lings’ rec’n. 





AO Ad 

O 0/1 






z • j 4 

St. Louis. 

75,000,000 

157,000.000 

6 

2 

2232 

2.50 

V icksburg. 


1,500,000 

I 



AO 

Altona, 'go ... . 

4,900,000 

1,500,000 

2 

\ 

3800 

• 

3-8 

London : 







Chelsea. 

11,800,000 

168,000,000 

• • • • 

14.2 



E. London... 

53,870,000 

738,000,000 

• • • • 

13-7 



G. Junction.. 

22,000,000 

77,000,000 

• • • • 

3-5 



Lambeth .... 

23,538,000 

153,000,000 

.... 

6-5 



N. River .... 

40,000,000 

203,000,000 

• • • • 

5 -i 



Southw. and 







Vauxh. 

44,000,000 

79,000,000 

• • • • 

1.8 



W. Middlesex 

20,150,000 

141,000,000 

• . . . 

7.0 




The frequency of cleaning will, of course, depend 
upon the amount of suspended matter carried by the 
water at different times and seasons, on the water con¬ 
sumption, and on other factors. At times, and under 





























SETTLING BAS/A r S. 


51 


some conditions, basins may go for a year or more 
without cleaning being necessary, or they may re¬ 
quire it at intervals of a few weeks. 

Form .—The form to be given to the basins will de¬ 
pend, probably, on the configuration of the ground. 
Where one shape can be used as well as another, the 
square or circle, which take less periphery to surround 
a given area than an oblong or oval shape, may be ad¬ 
vantageous. In large works basins are built in groups 
in order to have always sufficient storage to allow of 
one basin being cleaned without working the others 
at too high a rate. They are usually arranged side by 
side for the sake of economy of construction; the in¬ 
lets for raw water being at one end and the outlets for 
the settled water at the other. At Omaha, Neb., where 
the water is taken from the Missouri River, it was 
found that sometimes clarification would not follow 
sedimentation, even with periods of rest up to 72 
hours. The question was said to have finally been 
satisfactorily solved by causing the water to flow 
through a series of five settling basins of different 
sizes. The water flows from each basin to the next 
over wide, sharp-edged weirs, falling a height of from 
6 to 9 inches, in a thin sheet, by which means aeration 
is promoted, in order to counteract the tendency to 
bad odors caused by the necessarily long period of 
time occupied by the water in passing through the 
basins. This feature was covered by patents. 

Arrangements to Draw Off Water Longest in Stor¬ 
age .—In some places the basins are divided by longi¬ 
tudinal partitions in such a way as to force the water 


i 


52 


WATER FILTRATION- WORK'S. 


to take a circuitous course from the inlet to the out¬ 
let, and thus insure greater certainty that the water 
that has been in the basin longest will be removed 
first, and to prevent the direct washing of the water 
across the basin from the inlet to the outlet. In 
Frankfort-on-the-Main, Mr. William Lindley has pro¬ 
vided means to draw off the water first that has been 
longest in storage by a series of immersion plates, 
partitions extending across the basins, movable verti¬ 
cally in slots at each end, and slightly less in height 
than the depth of the water in the basins. If the water 
coming in from the supply main is warmer than that 
in the basins, the plates are drawn up so that the water 
to get out must go downward, thus forcing out first 
the water that has been longest in storage. If the 
supply-water is cooler than that in the basins, the im¬ 
mersion plates are forced to the bottom and the 
water is drawn off over their tops. 

Locations of Inlets and Outlets .—For continuous 
operation the inlet should be near the bottom, at one 
end, and the outlet near the top at the other end. If 
the basin is very long the inlet and outlet might both 
be from 3 to 4 feet above the bottom. The opening 
of the inlet should be large, or perhaps it would be 
better to have several, entering at points some dis¬ 
tance apart, in order to reduce the velocity of the en¬ 
tering water as much as possible, so as to deposit the 
heavy sediment near the inlets, and to improve the 
conditions of flow throught the basin. There is no 
objection to the inlet being at or near the bottom of 
the basin. The outlet should be at least 3 or 4 feet 


SETTLING BASINS. 


53 


below the surface, in order to exclude floating objects 
and to avoid the danger of clogging with ice. The 
successful practice of to-day indicates that floating 
arms and stand-pipes with many draw-off valves at 
dilferent elevations are useless refinements, likely to 
give much trouble in cold climates; it being generally 
perfectly satisfactory to have the outlet of large size 
some depth below the surface. In fact, the outlet may 
be placed low enough to be used on the fill and draw 
method, if desired. At the St. Louis and Ham¬ 
burg plants, both very large, the outlets are placed at 
but slight elevations above the bottoms. 

Construction. 

Bottoms .—As ordinarily built, after the excavations 
for the basins have been made, the bottom and side 
slopes, if the sides are not formed of masonry walls, 
are covered with an impervious clay-puddle carefully 
and thoroughly rammed and consolidated to prevent 
leakage. The puddle should vary in thickness accord¬ 
ing to the character of the bottom, the quality and 
composition of the clay, and the depth of the basins. 
Where the soil is firm and the puddle is a pure, clean 
clay mixed with about an equal quantity of gravel, a 
thickness of about 9 inches will suffice. If the puddle 
is made from a clay containing a considerable amount 
of micaceous material, a depth of even two feet may 
not be too much, if the water has to be pumped at 
considerable expense. The clay lining should be 
covered with a paving of brick, laid dry, or of con¬ 
crete, in large slabs, to protect the clay from erosion, 


54 


WATER FILTRATION WORKS . 


and to facilitate cleaning. On the slopes, where ice 
may form, and frost cause trouble, the brick paving 
should be bedded in Portland cement, or the slope¬ 
lining should consist of a layer of strong concrete. 

In case a good clay for puddle is not to be obtained 
without great expense, it may be necessary to use a 
lining of concrete 6 to 9 inches thick for the bottom 
and slopes. This has frequently been done with suc¬ 
cess. There is, however, great likelihood that such 
large surfaces of concrete may crack under tem¬ 
perature changes when the basins are emptied for 
cleaning and the bottom and slopes exposed to the 
hot sun for considerable periods of time. The danger 
from such cracking is not always great, but in case 
the subsoil when wet is of a nature to yield under 
pressure considerable settlement may take place 
along the cracks, and leaks of serious magnitude may 
follow. If the subsoil when wet is very firm and re¬ 
tentive such a danger would not be great, as the 
cracks might possibly silt themselves up again to a 
condition of water-tightness. 

Instead of using such expensive methods in the 
construction of settling basins, it may sometimes be 
satisfactory to form them along the bank of the river 
or lake from which the water is taken, by excavating 
the interior space with dredges and forming the em¬ 
bankment along the river side from the excavated 
sand or earth. The faces of the slopes, inside and 
outside, should be protected with a thick riprap of 
broken stone to prevent abrasion, and the necessary 
inlets and outlets for the regulation of the flow 


SETTLING BASINS. 


55 


through the basins should be provided. Such basins 
might be cleaned at small expense by means of a 
suction pump, mounted on a barge. This plan was 
contemplated in the settling basins proposed for the 
Torresdale filter plant on the Delaware River at 
Philadelphia.* 

Underdrainage .—In cases where the bottoms of the 
basins are lower than the water in the river, it may, if 
the land is porous, be necessary to underdrain the 
site. The drains should discharge into a sump, from 
which, in wet seasons, the water may be pumped, to 
prevent the possible breaking in of the lining, by the 
upward pressure of the ground-water when the basins 
are emptied for cleaning. If two adjoining basins 
are separated by a division wall of masonry, great 
care should be exercised in the placing of the puddle. 
This should be of increased thickness on each side of 
the wall, and should extend down the sides of it and 
under the footings, unless the latter be founded on 
rock or other impervious material. This precaution 
is necessary to prevent the blowing out of the bottom 
of a basin when its neighbor is emptied for cleaning 
or repairs. An accident of this kind happened several 
years ago to the St. Louis settling basins. 

Sides .—If the sides of the basin are to be of ma¬ 
sonry they should be designed according to the ordi¬ 
nary rules, as retaining walls, considering the basin 
empty. If the sides are simply the dressed faces of 


* Report on the Extension and Improvement of the Water- 
supply of the City of Philadelphia, 1899. Rudolph Hering, 
Joseph M. Wilson, and Samuel M. Gray. 




56 


WATER FILTRATION WORKS. 


the excavation or embankments, they should have a 
slope of about 2 horizontal to 1 vertical, excepting in 
very loose soils, when the slope should be increased 
to 3 to 1. 

Arrangements for Cleaning .—The bottom of each 
basin should have a longitudinal channel through the 
centre, sloping, as circumstances may make neces¬ 
sary, toward one end or the other, with a slope of 
about 1 in 500. The bottom surface should slope 
toward this channel with an inclination of about 1 in 
200, in order to facilitate the removal of the sedi¬ 
ment. If the basins are very large, and construction 
expensive, flatter slopes than these may be used. At 
the large basins at Hamburg the bottom slope longi¬ 
tudinally is only about 1 in 1750. At Omaha, Neb., 
the bottoms of the basins, instead of being sloped in 
only two directions, are formed of a series of de¬ 
pressions, toward which the sludge gravitates or may 
be pushed. The sludge is taken to the clean-out con¬ 
duit through a mud-valve at the lowest point of each 
depression. A system of four-inch water-mains, with 
convenient hose connections, supplies the water for 
washing out the basins. 

Regulating Apparatus .—At Hamburg the water of 
the Elbe is pumped into a large channel, which 
supplies all the basins. As the basins lie between this 
channel and the filters it is necessary to regulate both 
the inflow of water to the basins and the outflow to 
the filters in order, first, that the basins may not be 
overflowed, and, second, that the too rapid flow of 
clarified water to the filters may not cause the water 



Plate III. —Settling Basin, Albany, N. Y. View showing 
Inlet for Raw Water; Slope Paving; Concrete Bottom, 
and Method of Removing Sediment. 


57 

















SETTLING BASINS. 


59 


to stand too deeply on the surface of the filters. Each 
basin is filled through two branch-pipes, about 3 feet 
in diameter and at right angles in a horizontal plane, 
which join in a cast-iron vertical cylinder about 4 feet 
3 inches in diameter in the gate-house. The water 
from the canal is admitted to this cylinder by raising 
a double-seated valve, and then flows into the basin 
through the branch-pipes. When the water stands at 
the proper height in the basin the valve is closed. 

The water flows to the filters through a regulating 
house at the opposite end of the settling basin, in 
which is placed a double-seated valve operated by 
a float resting upon the surface of the water in the 
canal leading to the filters. This regulates the 
amount of water flowing to the filters in accordance 
with the amount needed. The water enters the 
house through 18 rectangular holes in the wall, about 
three feet above the bottom. The regulating valve 
can also be operated by hand. 

The basins have side slopes of 3 horizontal to 
1 vertical. They were built upon marshy ground 
and are underlaid with a thick layer of clay-puddle. 
The bottoms and sides are paved with brick, while 
concrete is employed for protecting the slopes in the 
zone where ice forms. 

At Albany, New York, the inlets are perforated 
with small holes above the water line of the basin, 
to promote the aeration of the water as it enters the 
basin. This is shown quite clearly in Plate III. 

In the English practice the inlet is frequently a bell- 
mouth pipe, delivering the water at or near the bot- 


6o 


WATER FILTRATION WORRTS. 


tom of the basin, and the outlet merely a pipe con¬ 
trolled by a valve. Sometimes the outlet will consist 
of a stand-pipe with several valves at different eleva¬ 
tions, or of a floating pipe, one end of which is main¬ 
tained at a certain depth below the surface by a float. 

Removal of Sediment .—If the basins are placed at 
such an elevation that they can be drained by 
gravity the removal of the sediment is easily ac¬ 
complished by washing and pushing it toward the 
outlet at one end. This outlet should be large and 
should be closed by a penstock or sluice-valve oper¬ 
ated from above by a spindle. 

If the basins are to be operated on the continuous 
plan, it would be preferable to slope the bottom 
downward toward the inlet end of the basin and lo¬ 
cate the outlet for sediment near the inlet. In or¬ 
der to facilitate the removal of the sediment it might 
be advantageous to provide a supply-main, with wa¬ 
ter under pressure, along the opposite end of the 
basin from the inlet, provided with valves and nipples 
for discharging water into the basin at the upper end, 
and thus supplying a current for the removal of the 
sediment by water-carriage. If the basins are to be 
operated on the fill-and-draw method the outlets for 
sediment might be preferably located on the opposite 
end of the basins from the inlets for raw water, and 
the bottom should then slope toward the outlet. In 
this case the necessity does not exist for the extra 
supply-main for washing out the basins, as the raw 
water may be used for that purpose. A very con¬ 
venient arrangement for washing out the sediment 


SETTLING BASINS. 


61 


is in use in St. Louis. It consists of a movable siphon 
by which a stream can be siphoned out of a full basin 
for washing a contiguous empty one. The siphon is 
moved along as the washing progresses. Other 
means have to be provided for the basins on the ends 
of the series. 

If the basins are placed so low that they cannot be 
drained by gravity, as at Antwerp, Shanghai, Rotter¬ 
dam and at some of the London works, it will be 
necessary to construct in each basin a sump to which 
the sediment may be washed, and from which it may 
be removed by centrifugal or other pumping ma¬ 
chinery. 

When the outfall end of the clean-out conduit is 
subject to submersion by floods or tides a tide-flap 
should be placed over the end to protect it from 
silting up during periods of high water. 

Roofing .—There is no necessity in this country for 
roofing over large settling basins. The only reasons 
which can be urged for such a practice would be to 
prevent the formation of ice, to protect them from the 
winds, and from light. Basins, as usually built, are of 
such depth that the formation of ice will not cause 
serious inconvenience; the reduction of their capa¬ 
city, by the ice, will not be significant, because, dur¬ 
ing cold months, the draft will generally be light, and 
the water will, as a rule, contain less suspended mat¬ 
ter than in the summer months. The effect of the wind 
on the rate of sedimentation will be very slight, as 
the action of waves in causing eddies below the sur¬ 
face is quite insignificant, as a rule, in such small areas 


62 


WATER FILTRATION WORKS. 


and in waters of such small depth. If it should be 
found, however, that there was a retardation of sedi¬ 
mentation, or that the waves were apt to damage the 
walls or slopes of the basins, the trouble could easily 
be remedied by a series of floating spars resting upon 
the surface of the water. This expedient was resorted 
to with success in the very large sewage precipitation 
tanks at Manchester, England, which are in a posi¬ 
tion exposed to very severe winds. 

The necessity of protecting basins from the light 
vanishes if their storage capacity does not exceed a 
day or two’s supply; if objectionable odors or growths 
of algae should result, on longer storage, a simple 
treatment by aeration, before storage, might be suf¬ 
ficient to remove the objectionable qualities. As to 
whether the benefits arising from covering the set¬ 
tling basins, due to maintaining the water at a higher 
temperature in winter, and thus favoring more rapid 
sedimentation, would offset the increased cost of 
construction, and also of operation, it may be, in the 
light of our present experience, answered in the neg¬ 
ative. 

Cost .—The cost of sedimentation basins depends 
upon so many local conditions and circumstances, 
that a comparison of the data of different basins 
would give a very wide range of costs. Basins of 
about 3,000,000 gallons capacity, with concrete bot¬ 
toms, 12 inches thick, on 12 inches of puddle, and 
with concrete sidewalls, including the iron work, 
masonry, intake well and connections, but excluding 
the cost of land, will cost not far from $9,000 per . 


SETTLING BASINS. 


63 


million gallons of capacity. Those in which the bot¬ 
toms and sides are puddled with clay and paved with 
brick will probably cost less than this; and others in 
which the bottoms are of concrete, laid on a puddle- 
bed, with asphalted joints, may cost more. The aver¬ 
age actual cost of the reservoirs of the Philadelphia 
water-supply has been about $4,051 per million gal¬ 
lons of capacity, ranging from about $3,300 to 
$4,300. 

Operation. 

The water should be taken into the basins when 
in its best condition. In tidal streams, as already 
noted, there will generally be times when the wa¬ 
ter will be more pure than at others. Therefore, un¬ 
der these circumstances, the basins should, if possible, 
be so arranged and placed that they may be flooded 
very rapidly, and the intake and conduits should 
be correspondingly large. Where there is no appar¬ 
ent change of quality in the water, due to a periodi¬ 
cally recurring cause, the water may be taken from 
the river from near the surface. 

Rate of Flow .—If the settling basins are operated 
continuously, local conditions must determine how 
the rates of flow should be regulated. Where the 
basins are joined to a common conduit, leading to 
pumps, the regulation of inflow and outflow can 
safely be effected by the attendants. Their duty in 
this case would be to see that certain maximum and 
minimum depths of water in the basins and conduits 
were not passed, and that the rate of delivery from 
each basin did not exceed the limit determine d upon 


6 4 


WATER FILTRATION WORKS. 


in the design. The fluctuating draft from the city, 
varying with the seasons, days and times of day, 
makes the work thrown upon the basins very variable 
unless the water goes to storage reservoirs before 
being: delivered into the mains. Where sedimenta- 
tion is not to be followed by filtration it is not often 
that this could be the case, as in such works the ba¬ 
sins themselves must provide the storage to meet this 
fluctuation. 

The labor necessary to effect the regulation for 
the fill-and-draw method amounts in large plants 
to about 25 cents per million gallons. For the 
continuous-flow method it is less than half of this, as 
it may be done by automatic apparatus similar to 
that already described as being in use in Hamburg. 

Amount of Sediment to be Expected .—The amount of 
matter that will subside from a turbid water is very 
difficult to estimate, analyses even affording but little 
guide as to what may be expected. This may be seen 
from the data compiled in Table VII. 


TABLE VII. 


River and Place of Observation. 

Cu. yds. 
Sediment 
per Million 
Gallons. 

Observer. 

Date. 

Mississippi, St. Louis .... 

g.I 

McMath. 

1879 

< « H i i 

3-3 

Miss. River Comm. 

80-81 

“ Helena. 

3-9 

Johnson. 

1879 

Hannibal .... 

.82 

Miss. River Comm. 

1880 

“ Prescott. 

.60 

Clarence Delafield. 

80-81 

Clayton. 

.18 

4 4 i < 

80-81 

Sacramento River. 

27.30 

Le Conte. 

1879 

Garonne, Bordeaux. 

6. 20 

M. R. de Volontat. 

1874 

i ( i i 

•59 

■ • «t <1 <1 

1S75 

Mississippi R.,Vicksburg. 

5 • 20 

C. R. McFarland. 

1895 





















SETTLING BASINS . 


65 


Table VIII shows the analyses of the Garonne 
waters at Bordeaux. The quantities are averages for 
each month from 1870 to 1874, as determined from 
samples taken from the surface of the river at high 
tide. 

TABLE VIII. 


Month. 

Cu. ft. of Sediment 
per Million Gals. 

Month. 

Cu. ft. of Sediment 
per Million Gals. 

January. 

31-26 


49.26 



February. 

31.68 

August. 

104-75 

March. 

18.32 

September.... 

171.19 

A pril. 

17 Q T 

Ortoher. 

147 80 

May. 

16.07 

November .... 

81-53 

June. 

I 7-58 

December. 

25-79 


The amount of sediment removed yearly by man¬ 
ual labor, from 1884 to 1895, from the settling basins 
at St. Louis, is given in Table IX. 


TABLE IX. 


Year. 

Cu. yds. of Sedi¬ 
ment Removed 
from Basins. 

Millions of 
Gallons Pumped 
to Basins. 

Cu. yds. of Sedi¬ 
ment per Million 
Gallons. 

Cost of Remov¬ 
ing Sediment. 

1884-5 

153,000 

9,564 

15-997 

$3276.00 

1885-6 

109,000 

9,925 

10.982 

2195.36 

1886-7 

124,000 

10,979 

11.294 

2137.50 

1887-8 

143,OOO 

11,665 

12.336 

1865.41 

1888-9 

174,000 

11,644 

14 - 9-13 

2869.60 

1889-90 

144,750 

n ,939 

12.124 

I386.OO 

1890-I 

207,800 

13,178 

15-768 

I4II.20 

1891-2 

210,600 

14,602 

14.423 

2286.40 

1892-3 

160,000 

16,448 

9-725 

2810.88 

1893-4 

148,000 

17,448 

8.482 

3519.20 

1894-5 

208,000 

16,257 

12.794 

2668.20 


The actual quantity of suspended matter removed 
by subsidence has been from three tenths to four 
tenths in excess of these quantities. 


































66 


WATER FILTRATION WORKS. 


Depth of Sediment to he Provided for .—The depth of 
sediment which should be allowed to collect in the 
basins before cleaning them will vary according to 
the nature of the sediment and the design of the 
basins. If the sediment is very heavy the basins may 
require more frequent cleaning than if it is of lighter 
specific gravity. At Altona it is reported that two 
feet of sediment collected in the basins in three 
months. At Hamburg provision is made for a depth 
of about three feet of sediment, which here is of light 
specific gravity. At Antwerp about one foot in depth 
is allowed for. 

Periods of Cleaning .—Table X, compiled from the 
annual reports of the Water Commissioner of St. 
Louis, illustrates some of the practical considerations 
that govern the times of cleaning the basins at that 
city. 

table x. 


Date. 

No. 1 . 

No. 2 . 

No. 3 . 

No. 4 . 

Cost. 

a 

b 

a 

b 

a 

b 

a 

b 

A oril. 180^ ...... 







36 

24 

$ 165.00 
572.20 
1296.00 

418.80 

312.80 

227.20 

527.20 
781.60 

743-40 

864.80 
278.40 

July. 

50 

IO 

35 

7 





August. 

September. 

66 

48 

66 

48 

13 

53 

9 

39 

October. 

36 

14 

46 

70 

50 

18 

24 

8 

24 

40 

30 

9 

20 

10 

20 

46 

78 

54 

18 

12 

6 

10 

24 

48 

36 

9 



November. 

March, 1894. 

May. 

July. 

October. 

March, 1895. 

20 

20 

46 

78 

54 

20 

12 

IO 

24 

46 

36 

IO 

18 

14 

40 

78 

54 

10 

8 

20 

46 

36 

294 

177 

312 

| 193 

304 

186 

306 

192 

6187.40 


Column a gives total depth in inches of sediment in basin. 
Column b gives depth of sediment removed by manual labor. 
























































SETTLING BASINS. 


67 


The total amount of sediment collected from April, 
1893, to April, 1894, was 222,000 cubic yards, of 
which 148,000 cubic yards were removed by manual 
labor. For the year 1894-5 the figures were 356,000 
and 208,000 respectively. 

A study of this table shows that the greatest 
amount of sediment is collected, and therefore the 
most frequent cleaning is needed in the summer 
months, from March to October. The maximum 
rate of precipitation occurs about July, which also 
corresponds in general to the periods of high water, 
and to the time of the year when the water consump¬ 
tion is greatest. From October to March the river 
is low, excepting for the flashy rise due to the Jan¬ 
uary thaws, the consumption of water is below the 
average and the amount of sediment collected very 
small. The times of cleaning, therefore, beginning 
with the month of March, are at intervals of two 
months, two months, three months and five months. 

Amount of Water Necessary for Cleaning .—The 
amount of water necessary for cleaning out a basin 
will depend upon the slope of the bottom, the nature 
of the sediment, the judgment of the men, and the 
manner in which the cleaning-water is used. The 
work of removing the sediment is done partly by the 
water and partly by hand. 

With a certain cross-section of channel in the cen¬ 
tre of the basins and a given slope, it is possible to 
move only a certain quantity of sediment in the water 
used for washing. Basins in which the bottoms are 
comparatively flat will, therefore, take a greater 


68 WA TER FILTRATION IVOR NS. 

quantity of water and a longer time to clean than 
those in which the inclination is greater. Ihere are 
no available published data concerning the absolute 
amount of suspended matter that can be carried in 
water flowing in open troughs or channels of different 
dimensions and at different slopes. Probably, the 
more finely comminuted the matter, the greater abso¬ 
lute weight of it can be carried by the water at any 

given velocity. The removal of the sediment by wa- 

✓ 

ter-carriage is brought about by two agencies—the 
power of the water to carry a part of the matter in 
suspension and its power to roll on the bottom parti¬ 
cles larger than it can carry in suspension. Both of 
these effects are produced at a loss of energy. Veloc¬ 
ities of flow in the clean-out conduit, calculated ac¬ 
cording to the usual rules, will, therefore, be too great. 
If the slope of the conduit were proportioned so that 
the velocity for clean water would be from about io 
to 12 feet per second when running half full, it is prob¬ 
able that the sediment could be carried through it 
without too great an allowance of flushing-water. 
This velocity would probably carry off a sandy sedi¬ 
ment to the extent of about 5 per cent, of the volume 
of the wash-water. If the sediment were more earthy, 
possibly as much as 10 per cent, could be.carried out. 
This would be of the consistency of the average sew¬ 
age-sludge resulting from chemical deposition. 

The amount of sediment carried in flowing rivers is 
very variable. Such measurements as have been re¬ 
corded show a range of from about one two-hun- 


Plate IV. —Albany Filtration Plant. General View of Settling Basin, showing 

Removal of Sediment deposited from the Water. 













SETTLING BASINS. 71 

dredths of i per cent, to about i per cent, of the vol¬ 
ume of flowing water. 

The amount of water used in washing the sediment 
out of the basins will, therefore, probably amount to 
from i o to 20 times the volume of sediment removed. 

Methods of Cleaning .—The cleaning is done by the 
action of flowing water, combined with labor, both so 
directed that the sediment is, pushed and washed into 
the central channel and finally into the clean-out con¬ 
duit. The expense of cleaning is therefore divided 
into two parts—wages of laborers and cost of wash- 
water—because of the water having to be pumped. 
The expense of pumpage is present in every case but 
one. If the basins are placed lower than the river, so 
that the water flows into them, the expense of pump¬ 
ing falls on the sediment-laden water, which must be 
removed from the basins. The only case where the 
expense of pumping can be avoided entirely is where 
the settling reservoirs are located at the site of a fall, 
or dam of considerable height, so that the water may 
be flooded into the basins and the wash-water allowed 
to flow out by gravity. This is a condition, however, 
that will rarely be realized. 

The method of cleaning the settling basins at Al¬ 
bany, N. Y., is illustrated in the photographic views, 
Plates III and IV. 

In cleaning the St. Louis basins the upper semi¬ 
fluid part of the sediment, about three tenths to four 
tenths of the total amount in the basins, goes out 
without the necessity of manual labor in its removal. 
The remaining six tenths to seven tenths is removed 


< 


72 WATER FILTRATION WO RUTS. 

partly by water and partly by being pushed to the 
outlet with squeegees. 

Cost of Removing Sediment .—The cost of removing 
the sediment, per million gallons of water, will vary 
with the seasonal changes in the character of the raw 
water. Estimates of this sort, therefore, are difficult 
to make and can serve only as a rough approxi¬ 
mation. Mr. Wm. H. Lindley gives the cost of subsi¬ 
dence in covered reservoirs, in Germany, including 
interest and sinking fund, at from $1.80 to $2.25 per 
million gallons, of which from 50 to 60 per cent, is for 
interest and sinking fund. Taking the values given 
in the reports of the Water Commissioner of St. 
Louis for 1894 and 1895, the cost per cubic yard of 
sediment removed from the basins, for maintenance 
and cleaning, for the two years would be as given in 
Table XI. 


TABLE XI. 



1894 

1895 

Cents per cu, yd. 

Pav-roll, gatemen foremen, etc. 

2.1 

1.6 

2-3 

I .O 

1.4 

.8 

2.8 

1.0 

Pay-roll, labor cleaning basins. 

Repairs and maintenance of basins. 

Water used in cleaning (estimated by author) .... 

Total. 

7.0 

6.0 



Since 1884 the average amount of sediment re¬ 
moved from the water has been about 12.5 cubic 
yards per million gallons, which, at 7 cents per cubic 
yard, would make the cost about 87.5 cents per mill- 


















SETTLING BASINS. 


73 


ion gallons, exclusive of interest and sinking-fund 
charges. The charges for these items, per million 
gallons, will depend upon the amount of water clari¬ 
fied, that is, on the speed with which the water is 
passed through the basins. As they are now oper¬ 
ated, on the fill-and-draw method, this charge cannot 
be much less than about $3.00 per million gallons. It 
must be remembered, however, that the basins have 
a capacity for two days’ supply at maximum draft, 
and that if the consumption should greatly increase, 
the same basins would serve without it being neces¬ 
sary to increase their capacity, although certain 
changes in details might be advisable to reduce the 
cost of operation. When operated to their maximum 
capacity, the total average cost of removing the sedi¬ 
ment might be from $2.25 to $2.50 per million gal¬ 
lons of water passed through the basins. 

Relative Advantages of Fill-and-Drau) and Continu¬ 
ous Operation .—The principal advantage of the fill- 
and-draw method is that a more perfect quiescence of 
the water may be obtained, and for this reason, per¬ 
haps, a greater quantity of suspended matter may be 
precipitated in a given time. This advantage has not, 
however, in many works which have been executed, 
been found sufficiently great to counterbalance the 
disadvantages in point of cost of construction and 
cost of operation. If the sediment is heavy, and set¬ 
tles rapidly, the greatest bulk, under the continuous 
method, will subside near the point where the raw wa¬ 
ter enters the basin. Under the fill-and-draw method 
the sediment will be spread further away from the 


74 WATER FILTRATION WORK'S. 

inlet-pipes by the currents, as the basin fills. There¬ 
fore, if the clean-out conduit from the basin must be 
located near the inlet for raw water, the continuous- 
flow method will deposit the sediment where it will 
cost less for its removal than the fill-and-draw method. 
On the contrary, if the clean-out conduit is on the op¬ 
posite side of the basin the fill-and-draw method 
will be the most economical in point of cleaning. 
If the construction of the settling basins is pre¬ 
paratory to a process of filtration, still other consider¬ 
ations may have weight in their design. Local con¬ 
ditions will then have to decide whether their opera¬ 
tion should be continuous or on the fill-and-draw 
plan. If the basins can be placed higher than the fil¬ 
ters, it may be advantageous to use the fill-and-draw 
system; if not, it will generally be necessary to oper¬ 
ate them continuously, because, even if pumping has 
to be resorted to between the basins and the filters, it 
will be on the side of economy to reduce the lift on 
the pumps as much as possible. 


CHAPTER III. 


THE PURIFICATION OF WATER BY SLOW SAND- 

FILTRATION. 

INTRODUCTION. 

Types of Filters Used for Filtration of Municipal Sup¬ 
plies. —Filtration, in the sense in which the word is 
used in this work, has for its object the removal from 
water of objectionable polluting matter that cannot 
be economically taken out by simple subsidence, or 
by chemical treatment. The successful filtration pro¬ 
cesses for purifying the water-supplies of cities and 
towns may be separated into three classes. The dis¬ 
tinctive characteristics of these classes are as follows: 
In one, first adopted in England, the water is filtered 
slowly through beds of sand; filters of this type are 
called English Filters, Slow Filters or Slow Sand-fil¬ 
ters. The second type, a distinctively American in¬ 
vention, filters the water rapidly through beds of 
sand, a coagulant having first been added to the w r a- 
ter; filters of this kind are called American Filters, 
Mechanical Filters or Rapid Sand-filters. The third 
type filters the water through a strainer of fine mesh, 
such as porcelain, concrete slabs, etc. All these meth¬ 
ods are in use. For the sake of uniformity, in the pres¬ 
ent work the terms Rapid and Slow Sand-filters will 

75 


j6 WA TER FIL TEA TION WORKS. 

be used in referring to the first two types, because 
they are short, distinctive and sufficiently exact. 

Slow Sand-filtration .—The process of slow sand- 
filtration consists of passing the water downward by 
gravity through beds of sand of certain depth, and 
with certain restrictions as to velocity and manipula¬ 
tion that experience has shown to be necessary. By 
this process most of the suspended matters in the 
water, including nearly all of the bacteria, are re¬ 
tained upon the surface of the sand; most of the re¬ 
maining bacteria are destroyed in the top layers of 
the filter, while a portion of the dissolved organic 
matter in the water is converted, by chemical acdon, 
into inorganic compounds. 

Rapid Sand-filtration .—The process of rapid sand- 
filtration consists of passing the water downward at 
a rapid rate through small beds of sand, a certain 
amount of coagulating material having been first in¬ 
troduced into the water to assist in forming a scum 
on the surface of the sand and a film between the 
grains of sand in the bed. The bacteria and sus¬ 
pended matters in the water are largely retained in 
the filter-bed. The coagulant may also reduce the 
color and dissolved organic matter in the water to a 
much greater extent than would be possible with 
slow sand-filters. 

Which of these methods of purification is prefer¬ 
able, in any given case, must be determined from care¬ 
ful considerations of the quality and character of the 
water, the results desired and the relative costs of the 

processes both for installation and operation. 


PURIFICATION BY SLOW SAND-FILTRATION. 77 


THEORY OF SLOW SAND-FILTRATION. 

The foreign substances carried in water are either 
mineral or organic, and they are dependent, to a cer¬ 
tain degree, on each other. The organic matter is 
found first as living organisms, vegetable or animal, 
which float or have the power to move about in wa¬ 
ter; second, as the products of organic life, such as 
albumen, urea and tissue, which may be dissolved in 
the water or suspended in it, and third, as products 
of the decomposition of organic matter. In the lat¬ 
ter class belong the salts of ammonia and of carbonic 
and nitric acids, which are absorbed by growing vege¬ 
tation as food. The carbon and nitrogen in organic 
matter are constantly changing from organic to min¬ 
eral matter and back again. The organic matter 
found in water consists mainly of carbon, hydrogen, 
nitrogen and oxygen. The process of decomposition 
may be said, in a general way, to consist of first the 
oxidation of the carbon, which leaves the nitrogen 
combined with hydrogen in the form of ammonia, 
and subsequently the union of the uncombined oxy¬ 
gen with the ammonia, converting it into nitric acid 
and water. This series of changes requires the pres¬ 
ence of oxygen and of some earthy or alkaline base 
in the water with which the acids can combine, when 
formed. Further, the presence of certain micro-or¬ 
ganisms is necessary to initiate and carry the process 
through to completion. 

In surface waters there are, therefore, constantly 
going on two actions, assisted by contact with the 


7 8 


WATER FILTRATION WORKS. 


air and the action of the sun’s light and heat. These 
are the oxidation of the elements of the organic mat¬ 
ter, and their absorption by the various forms of vege¬ 
tal and animal life. This process only goes on in the 
presence of light. In pure ground-waters we fail to 
find the presence of nitrates, but in ground-waters 
previously polluted, and in the bottoms of deep ponds, 
reservoirs or lakes we often find, due to the absence 
of uncombined oxygen and to the absence of light, 
the presence of free ammonia and nitrites, interme¬ 
diate products of the regeneration of decaying or¬ 
ganic matter. The plant-life which results from the 
absorption of the oxidized ammonia is called in chem¬ 
ical analyses, the albumenoid ammonia. 

Shallow stagnant bodies of water, which in the heat 
of summer are full of animal and vegetal life, become 
foul in time because decay gets ahead of growth, and 
the products of decomposition accumulate. 

The color acquired by surface waters, apart from 
turbidity, is derived from leaves, grass, peat, etc., by 
long contact. It contains considerable nitrogen, and 
is usually very stable in character. For the removal 
of this matter it is necessary to treat the water with 
hydrate of aluminum, which combines with the color¬ 
ing matter and gives a clear, colorless water on the 
precipitation of the coagulant, or its removal by rap¬ 
idly operated filters. 

Pure water should have no odor. If the odor is 
caused by dissolved gases, it will leave when the wa¬ 
ter is boiled. If it comes from suspended or dissolved 
organic matter, it may vanish when the water is 


PURIFICATION BY SLOW SAND-FILTRATION. 79 

boiled, but may again develop. The odors from sus¬ 
pended organic matter and vegetation may some¬ 
times come from the decay of the matter, but often 
they are caused by the organisms themselves. Some¬ 
times the removal of odors is a difficult matter, re¬ 
quiring a special line of treatment. 

As stated before, the change of the decaying mat¬ 
ter from organic nitrogen into the salts of nitric acid 
can only be brought about in the presence of bacteria. 
The fact had long been known, but it was not until 
about 1890 that it was possible to isolate the nitrify¬ 
ing organism. In that year, by the independent la¬ 
bors of Edwin O. Jordan and Mrs. Ellen H. Richards, 
of the Massachusetts State Board of Health, Dr. 
Percy F. Frankland and Grace Frankland and Wino¬ 
gradsky, abroad, the organism was isolated; since that 
time much intelligent investigation has been under¬ 
taken to determine the conditions which are most fa¬ 
vorable for the life, propagation and activity of the 
organism. 

The organism is present and active in the presence 
of oxygen, in all normal surface waters and probably 
also in falling rain. Among the conditions which are 
essential to the activity of the organism are the pres¬ 
ence of oxygen, organic matter, moisture and some 
alkali and a temperature suitable to foster the growth 
of vegetation. In slowly passing water containing 
these necessary ingredients through beds of sand, 
the conditions for rapid nitrification are gradually es¬ 
tablished. The nitrifying organisms in the applied 
water become attached to the sand grains, mostly in 


8o 


WATER FILTRATION WORKS. 


the upper layers of the sand, and attack the organic 
matter in the water, which, to a considerable degree, 
appears to unite with certain constituents of the fil¬ 
tering materials. The organic matter is resolved 
finally into soluble mineral salts, which pass out in the 
effluent. The conditions under which the most per¬ 
fect chemical purification takes place seem to be 
also the most favorable for the removal of the bac¬ 
teria in the applied water. The cause of the death 
and destruction of the bacteria may lie partly in the 
absorption of the oxygen of the applied water in the 
process of nitrification, but probably they are them¬ 
selves oxydized the same as other organic matter. It 
cannot be said they die from lack of food-supply or 
lack of oxygen, for there is generally a sufficient 
amount of ammonia in the effluents of filters to sup¬ 
port a considerable bacterial life; and it is known that 
there are certain species of bacteria that can live with¬ 
out the presence of oxygen. 

Action of Slow Sand-filters .—Recent investigations 
have demonstrated that in slow sand-filters in efficient 
service, showing a normal reduction of bacteria, a film 
of gelatinous material forms around the sand grains 
whereby most of the bacteria are mechanically re¬ 
tained under conditions that are not favorable for 
their existence. This gelatinous material is com¬ 
posed probably, in part, of dead or resting bacteria. 

Efficiency .—In discussing the results obtained by 
slow sandrfiltration there are three phases which 
should be considered; these are: bacterial efficiency, 
bacterial purification and hygienic efficiency. As the 


PURIFICATION BY SLOW SAND-FILTRATION. 8 1 

result of the experience of many years, it is known 
that the number of bacteria found in the effluents of 
slow sand-filters does not necessarily represent the 
number which have passed through with the water, 
and hence bacteriological analyses of filter-effluents 
may not be a correct index of the percentage re¬ 
moval of the bacteria. A large number, and in some 
cases all, of the bacteria found in the effluent, grow 
in the lower part of the filters and the underdrains, 
and there is as yet much difficulty in distinguishing 
between the latter and those which pass through with 
the water. Plagge * holds the view that even dis¬ 
ease germs may multiply in badly managed filters. 

The bacterial efficiency is the percentage which the 
number of bacteria found in the effluent water is 
of the number of bacteria in the raw water. The 
bacterial purification is the percentage which the 
bacteria actually removed by filtration is of the num¬ 
ber of bacteria in the water applied, and is consider¬ 
ably higher than the bacterial efficiency. The ex¬ 
periments with special growths of bacteria at the 
Lawrence Experiment Station, in 1894 and 1895, in¬ 
dicate that the normal bacterial purification from 
slow filtration ranges from 99 to 100 per cent. The 
hygienic efficiency is regarded as the percentage re¬ 
moval by filtration of the bacteria capable of produc¬ 
ing disease. The hygienic efficiency is probably fully 
as great as the bacterial purification. 

* Untersuchungen iiber Wasserfilter. Veroffentl. aus dem Ge- 
biete des Militar-Sanitatswesens. Med. Abth. des koenigl. 
preuss. Kriegsministerium. Berlin, 1895 . 



82 WATER FILTRATION WORKS . 

The percentage basis of expressing bacterial effi¬ 
ciency is unfair because with water low in bacteria 
the percentage will be very high, but with polluted 
water it may still be high and yet allow a great num¬ 
ber of bacteria to appear in the effluent. The German 
standard of ioo per c.c. seems to be based on a more 
rational idea, but this is also open to the objection that 
it is not universally applicable. If, for instance, the 
water were sewage polluted there might be many 
pathogenic bacteria in this ioo, while if the water 
were not sewage polluted, but contained several hun¬ 
dred of the ordinary water bacteria, it would be per¬ 
fectly unobjectionable. Such results must, there¬ 
fore, be interpreted with a knowledge of the charac¬ 
ter of the raw water as to sources of pollution. 

Influence of Character of Water .—The influence of 
the character of the water upon the results of slow 
sand-filtration is very decided. The available infor¬ 
mation shows clearly that there are some waters sat¬ 
urated with oxygen and containing small amounts of 
organic matter, which may be successfully purified by 
continuous filtration. On the other hand water con¬ 
taining very little or no free or dissolved oxygen, 
and large amounts of organic matter, cannot be puri¬ 
fied successfully by the continuous method, but will 
require an intermittent application of the water to the 
filters in small doses whereby a sufficient amount of 
oxygen is carried down into the sand to effect the 
requisite oxidation. 

The results obtainable, therefore, in the filtration of 
a polluted water may vary with seasonal changes, ac- 


PURIFICATION BY SLOW SAND-FILTRATION. 83 

cording to the amount of free oxygen in the water. 
When the oxygen is high the rate of filtration may 
also be high. The amount of oxygen present in the 
water may be an indication of whether the water 
should be filtered intermittently or continuously. 
The experience at the Lawrence, Mass., Experiment 
Station has shown that free oxygen is never absent 
from the effluents of slow sand-filters at the station, 
although, at times, the percentage is very low, par¬ 
ticularly in the filters operated continuously. The 
fact that the amount of free oxygen in water is least 
in summer weather, when the organisms of nitrifica¬ 
tion are most active, is significant. In Lawrence the 
percentage of dissolved oxygen in the Merrimac 
River and in the effluents of the water-filters de¬ 
creases gradually from the winter months to the mid¬ 
dle of September, and then gradually increases again 
as the winter months return. It is also noted that the 
effluents from the intermittent filters contain, almost 
uniformly, a higher percentage of dissolved oxygen 
than the effluents from the continuous filters. The 
general results obtained from the Lawrence experi¬ 
ments indicate that in the treatment of the Merrimac 
River water by slow sand-filtration it is-possible to re¬ 
move all the suspended matter, and a variable amount 
of the color and dissolved organic matter, and that 
old filters are as efficient as new in removing albu- 
menoid ammonia. The experience in regard to the 
removal of suspended matter at other experiment 
stations has shown, however, that slow sand-filters 
may fail to give satisfactory results in this regard. 


84 WA TER FILTRATION IVOR NS. 

Influence of the Size and Character of the Sand on the 
Efficiency of Slow Sand-filtration. —The physical char¬ 
acteristics of sand may be determined by sifting sev¬ 
eral samples through a series of sieves of different 
meshes, and then determining the percentage by 
weight of each size and the relations the different 
samples bear to each other. Using the nomenclature 
of the Massachusetts State Board of Health,* the Ef¬ 
fective Size of a sand is the size of the grain in milli¬ 
metres, such that io per cent, of the grains in the 
sample is finer than itself, and the Uniformity Co¬ 
efficient expresses the ratio of the size of grain such 
that 60 per cent, is finer than itself to the size such 
that io per cent, is finer than itself. Since the purifi¬ 
cation in the filter is brought about by the passage of 
the water between the sand grains, it is evident that 
the presence of large stones in the sand will not add 
to its value; the smaller the percentage of particles of 
larger grain than those of the effective size, the less 
waste material there will be in the filter, and the more 
uniform will be the passage of the water through it 
in all parts of the beds, both as to velocity and as to 
quantity. 

Influence of Compacting of Sand. —The resistance to 
the motion of the water through the sand, due to the 
compacting of the surface under service, gradually, 
to a slight extent, reduces the capacity of a slow sand- 
filter plant. This is caused partly by the settling of 


* For methods of analyzing sands, see article by Allen Hazen, 
in Report of Mass. State Board of Health, 1892. 



PURIFICATION BY SLOW SAND-FILTRATION. 85 

the sand in the water and the compacting of the sur¬ 
face by the workmen in cleaning. 

Sand, to be suitable for filter purposes, should be 
free from clay or calcareous materials, as these have 
a tendency to cement the sand grains together and 
produce other disturbing elements tending to reduce 
the efficiency, both by increasing the frictional resist¬ 
ances and by producing sub-surface clogging. The 
grains of sand should also be as uniform in size as 
possible, because the greater the variation in size, for 
any given effective size, the more compactly the sand 
will settle under the action of the flowing water, and 
the greater the frictional resistances will become. 
The filling of the filters from below, as well as the es¬ 
cape of air upward through the sand, will tend to re¬ 
adjust the grains, and if there is a great variation in 
their size, they can pack more closely than if they are 
all of one size. 

The available information regarding the effect of 
the size of the sand grains on the efficiency of a given 
sand in removing bacteria, in a filter which has been 
in service a long time, shows little to warrant the be¬ 
lief that the efficiency depends much on the effective 
size, within certain limits. The experience at the 
Lawrence Experiment Station goes to show that the 
percentage of bacteria which will pass through filters 
with sands of effective sizes of .14 to .38 millimetres, 
which have been long in service, is practically inde¬ 
pendent of the effective size. (See Fig. 3.) The num¬ 
ber of bacteria in the effluent seems to depend more 
on the number in the applied water than upon any 


86 


WATER FILTRATION WORKS . 


other factor. Even sands with an effective size of .48 
millimetres show as high bacterial efficiency as the 
finer sands, but require a longer time to give normal 
results. Observations on filters of coarse sands, in 



RATE OF FILTRATION IN MILLION GALLONS PER ACRE PER DAY 
Fig. 3.—Effect of Size of Sand Grains on Efficiency of 

Filtration. 

operation since 1889, go to show that as they grow 
older in service, they resemble more and more 
filters of fine sand. The chief points, however, in 
which the size of the grains has the most influence are 
that filters of coarse sand require a longer time, after 
being placed in service, to yield effluents of normal 
bacterial contents, and they are more sensitive to dis¬ 
turbing influences than filters of fine sand. 

Influence of Depth of Filtering Materials .—The influ¬ 
ence of the depth of the filtering material on the effi¬ 
ciency of filtration is felt principally in the steadying 





















PURIFICATION BY SLOW SAND-FILTRATION. 87 

action afforded by deep layers on the velocity of flow 
of the water through the sand, and by the bacterial 
action which takes place in the lower part of deep fil¬ 
ters. While deep filters are more efficient than shal¬ 
low ones, the latter are fairly satisfactory under fa¬ 
vorable conditions. As far as the data now at 
hand can be interpreted, it seems that a depth of 12 
inches in a filter long in effective service, will give 
nearly as good results as a greater depth, provided 
there is no outside disturbing influence; but if such 
disturbance should occur, its effect upon the effi¬ 
ciency of filtration will be more marked and of longer 
duration than in the case of deep filters. 

Fig. 4, which shows the average results from an¬ 
alyses of the materials of ten filters 5 feet deep at the 
Lawrence Experiment Station, exhibits the accumu¬ 
lation of organic matter and bacteria in slow sand- 
filters in successful operation. Four of these filters 
were intermittent and six were of the continuous 
type. The diagram shows that the greatest amount 
of the work, in the retention of the bacteria and 
stored nitrogenous matter, is being done in the top 6 
or 8 inches of the filters, and that all but an insignifi¬ 
cant proportion of the bacteria and nitrogen are re¬ 
tained in the upper inch. As ihe depth below the sur¬ 
face increases the number of bacteria and percentage 
of stored nitrogen decrease very rapidly until a 
depth of about 1 foot is reached, and then more 
slowly, but still perceptibly up to about 3 feet or 
more. The stored nitrogen below this depth may 
represent, according to Mr. Clark, the normal quan- 


DEPTH OF SAND 


88 


WATER FILTRATION WORKS. 



Fig. 4.—Diagram Showing the Retention of Bacteria and 
Stored Nitrogen in Ten Slow Sand-filters at the Ex¬ 
periment Station, Lawrence, Mass. 




























































PURIFICATION BY SLOW SAND-FILTRATION. 89 

tity which existed before the filters were placed in 
operation. This nitrogenous matter in the filters is 
the film of gelatinous matter arranged around the 
grains of sand; its existence in the lower portions of 
deeper filters in part explains the greater and more 
uniform efficiency of deep filters in removing bacteria. 

Because of their greater sensibility to disturbing 
influences, filters of a depth of 1 or 2 feet would not 
be so reliable in operation as deep filters. Experi¬ 
ments made at Lawrence on scraping filters 2 feet 
deep and 5 feet deep respectively, showed that scrap¬ 
ing did not affect the number of bacteria in the 
effluent of the filter 5 feet deep, while in the shallow 
one scraping was almost invariably followed by a 
large increase in the number of bacteria passing 
through, and caused Bacteria Prodigiosis, applied 
with the water, to appear in the effluent for 3 or 4 
days following the scraping. Numerous other records 
testify to the greater reliability of deep filters, and 
good practice, in the light of this experience, would 
require that filter-beds be made from 4 to 5 feet 
deep, according to circumstances. 

The usual European practice is to give the filter¬ 
ing materials a depth of from 2 to 4 feet, and to al¬ 
low this depth to be diminished by repeated scrapings, 
as the beds clog, to from 1 to 2 feet. When the 
minimum allowable depth has been reached, the sand 
taken out in the periodical cleanings is replaced and 
the filter brought back to its original depth. In Ger¬ 
many the Imperial Board of Health has specified that 
the sand should never be reduced to less than 12 


90 


WATER FILTRATION WORKS. 


inches in depth by cleaning, and, when possible, a 
greater depth than this should be maintained. 

The effect of the uniformity coefficient and the 
size of the sand have already been discussed. There 
is another qualification necessary for effective oper¬ 
ation, respecting the filtering materials. That is, the 
necessity for exercising great care in the sorting and 
placing of the sand in the filter. Layers of fine sand 
or loam in the body of the filter must be guarded 
against, as they will cause sub-surface clogging, and 
therefore reduced efficiency. Such layers have been 
tried in Holland, and have been experimented with 
at Lawrence, always with the above result. It is ad¬ 
visable to have the sand as nearly uniform as possi¬ 
ble in size of grain from top to bottom of the filter¬ 
ing material, and to so place the sand in the beds that 
there will be no planes of lamination or layers of dif¬ 
ferent degrees of compactness. 

Effect of the Loss of Head Upon the Efficiency of Slow 
Sand-filters .—The difference of level between the 
height of the surface of the water on the filters and 
the height to which the water would rise in a vertical 
pipe attached to the outlet of the underdrains, when 
the filter is in operation, is called the Loss of Head. 
This loss of head measures the resistance offered to 
the passage of the water through the filter, and de¬ 
pends upon the quantity of water filtered per unit of 
time, the age of the filter and other causes. It 
has been the general European practice to limit this 
loss of head to from 24 to 30 inches, in the belief that 
high heads compact the sand and also cause local 


P URIFICA TION BY SLOW SA ND - FIL TEA TION. 91 

breaking of the fine sediment layer on the surface, 
thus permitting water to pass through at greatly in¬ 
creased rates with resulting reduced efficiency. 

The experience of recent years, however, at the 
Lawrence Experiment Station, has pointed to the 
conclusion that neither of these circumstances exer¬ 
cises an important influence toward deterioration in 
the bacterial efficiency in properly operated filters, 
when the loss of head is allowed to equal the com¬ 
bined depth of the sand and its covering of unfiltered 
water. In some cases abnormally great numbers of 
bacteria were obtained under high heads, but their 
presence was satisfactorily explained in most cases. 
Under some conditions, however, as found at Cin¬ 
cinnati by Mr. Geo. W. Fuller, a head greater than 
the depth of the water over the sand was found to be 
detrimental, because the water contained a large 
amount of air in solution which was liberated when 
the head became negative; and this, rising in the form 
of bubbles, disturbed the filtering materials and 
brought about reduced efficiency. Generally speak¬ 
ing, negative heads should be avoided when possi¬ 
ble, though their use may not always be unsatisfac¬ 
tory. In many of the European filters the loss of 
head is limited by the method of construction of the 
beds. At Berlin the limit is about 24 inches and 
at Hamburg about 28 inches. The idea is com¬ 
monly held abroad, however, that not only are high 
heads dangerous, but that after a limit of about 2 
feet has been reached the head will increase in a 
very much more rapid proportion than the quantity 


9 2 


WATER FILTRATION WORKS. 


of water filtered between scrapings. I can find no 
careful investigations of this subject, however, ex¬ 
cepting those of the Massachusetts State Board of 
Health. This is a question that vitally concerns the 
cost of operation, because the less frequently the fil¬ 
ters require cleaning, the less will be the cost of oper¬ 
ation. In removing the film of sediment on the sur¬ 
face of the filter practical considerations make it im¬ 
possible to remove less than a certain depth of the 
material at one time. This depth is, within limits, in¬ 
dependent of the quantity of dirt that has accumu¬ 
lated, and any expedient that will lengthen the period 
of time between scrapings will result in a correspond¬ 
ing reduction of the quantity of sand to be washed 
per unit of water filtered, as well as a reduction of 
area of filter necessarily out of use during cleaning. 
The use of high heads will therefore allow of a 
greater length of time between cleanings than low 
heads, in waters which can be successfully treated by 
slow sand-filters. The experiments with the Law¬ 
rence experimental filters seem to indicate that the 
quantity of Merrimac River water which can be fil¬ 
tered between scrapings is almost proportional to the 
maximum loss of head allowed, and to the quantity of 
water filtered per acre per day, up to about five mill¬ 
ion gallons, and that very fine sands require more fre¬ 
quent scraping than medium or coarse sands. 

The great difference in physical characteristics 
and chemical constituents of waters from different 
sources, and at different times of the year, makes it 
impossible to state that the use of high heads is 


PURIFICATION BY SLOW SAND-FILTRATION. 93 

always advisable from the point of efficient and eco¬ 
nomical operation. The indications, however, point 
to the advisability, in all cases, of studying carefully 
the particular water in question, at various seasons 
of the year, to determine what effect high heads 
would have and their bearing on the design of the 
works. 

Effect of the Depth of Water. —There are few avail¬ 
able data on the effect of allowing the water to stand 
at a considerable depth over the sand in the filters. 
Usually economical construction establishes the limit. 
This is ordinarily from 3 to 5 feet in the European 
filters; it is seldom less than 3 feet, particularly in 
open filters where ice is apt to form, and seldom more 
than 5 feet except when the thickness of the sand 
layer has been reduced by frequent scraping. It is 
not probable that very much greater depths would 
have any unfavorable effect, either on the ability of 
the filter to pass large quantities of water, at reason¬ 
able rates, or on its bacterial efficiency. 

Effect of the Rate of Filtration on the Bacterial Effi¬ 
ciency. —The European engineers generally incline to 
the belief that low rates of filtration are necessary to 
high efficiency. Thus, the rate allowed at Hamburg 
is 1.6 million gallons per acre per day, and at Berlin 
2.57 million gallons. Most of the other German 
works keep below this latter limit, while in the Eng¬ 
lish practice the rate is generally under two million 
gallons per acre per day. If it is possible to success¬ 
fully use higher rates than these it is evident that a 
saving may be made in the area of the filters, and 


94 


WATER FILTRATION WORKS. 


thus in the cost of construction, as well as in the oper¬ 
ating, interest and sinking-fund charges. We have 
evidence, in some cases, that rates very much higher 
than these have been successful. The question is one 
that must be specially decided for each locality. Thus 
at Zurich, Switzerland, the water is often compara¬ 
tively low in bacteria, but high in constituents for the 
formation of the surface film, and being free from tur¬ 
bidity, allows of rates at times exceeding ten million 
gallons per acre per day, with excellent results. At 
Lawrence the rates have occasionally been, with old 
filters, as high as ten million gallons per acre per day 
in successfully filtering the Merrimac River water. 
Such high rates, however, are not recommended for 
continuous use. 

As waters vary greatly in their chemical, bacterial 
and physical characteristics, and in the amount and 
fineness of sediment carried in suspension, no hard 
and fast rule can be made for the best allowable rate; 
this can only be approximated in advance by esti¬ 
mate and finally determined by actual experience. 
Waters which are normally very high in bacteria, or 
in organic matter, or which are deficient in the kind 
of organic matter necessary for the formation of the 
gelatinous film around the sand grains, or which con¬ 
tain a considerable amount of finely comminuted 
clay in suspension, will require lower rates than wa¬ 
ters of the opposite characters. We find this condi¬ 
tion prominently recognized in the European works. 
The Hamburg rate of 1.6 million gallons per acre 
daily for the black, muddy, polluted water of the Elbe, 



PURIFICATION BY SLOW SAND-FILTRATION. 95 

after from 15 to 30 hours of settlement; the Berlin 
rate of 2.57 for the ordinarily clear waters of the Spree 
and Havel, and the Zurich rate of about 7.5 million 
gallons per acre per day for the perfectly clear lake- 
water, are probably the result of experience with sat¬ 
isfactory bacterial purification and economy of oper¬ 
ation in view. With the water of the Merrimac 
River, at the Lawrence Experiment Station, perfectly 
satisfactory purification has been attained for long 
periods of time in filters of considerable age, with 
rates up to 7 million gallons per acre per day, and 
in some cases even with rates reaching 10 million 
gallons. 

The deleterious effects of high rates will be felt very 
much more in filters with thin than with thick sand 
layers, and also the effects will be more noticeable in 
a new filter than in one which has been in service 
many months. 

Effects of Sudden Changes in the Rate of Filtration .— 
The results obtained at the Lawrence Experiment 
Station indicate that sudden changes of rate should 
be avoided, as they are likely to directly affect the 
bacterial purification. Generally speaking, an in¬ 
crease of rate above the normal at which the filter has 
been operating for some time is attended by a marked 
increase in the number of bacteria in the effluent for 
periods of from several hours to several days, and this 
increase in number usually follows the change of rate 
in about such a time as to suggest that the multiplica¬ 
tion of bacteria in the effluent is due largely to their 
detachment from the sand grains near the surface of 


g6 WA TER FIL TRA TION WORKS. 

the filter. A comparatively sudden increase of rate 
from below the normal to the normal rate, as in in¬ 
termittent filters, is not, as a rule, in filters of consid¬ 
erable age followed by a diminution of efficiency. 
Violent changes should at all times be avoided be¬ 
cause they may result in disturbing mechanically the 
filtering materials, and consequently directly affect 
the efficiency of the process. 

Influence of the Age of Slozv Filters on their Bacte¬ 
rial Efficiency .—When a new filter is first placed in 
operation it does not at once begin to yield pure wa¬ 
ter. It generally requires from one to two months to 
establish its proper biological construction and give 
an effluent containing a low number of bacteria. This 
biological construction consists principally in the ac¬ 
cumulation of organic and mineral matter, in a gelat¬ 
inous film, around the sand grains, and in the de¬ 
velopment of the nitrifying organisms by which the 
organic matter and the bacteria are retained and de¬ 
stroyed. This power of retaining and destroying the 
bacteria in the applied water increases with the 
length of time the filter has been in operation. This 
increased bacterial efficiency, caused by greater 
length of service, is much more apparent in filters 
of coarse sand than in those constructed with fine 
sand, and, indeed, as filters of coarse sand increase 
in age, they resemble, both in bacterial efficiency and 
in ability to pass given quantities of water, filters of 
fine sand. This is probably due, on the authority of 
the Massachusetts State Board of Health, to the 
more closely compacted condition of the sand, caused 


PURIFICATION BY SLOW SAND-FILTRATION. 97 

by a readjustment of the sand grains in refilling the 
filters from below, by the washing in of fine sedi¬ 
ment, and the retention of masses of organic and min¬ 
eral matter on the sand grains, which in reality re¬ 
duce the effective size of the sand. 

Influence of Scraping on the Bacterial Efficiency of 
Slow Sand-filters .—The theory had, until recently, 
been held in Europe that the effectiveness of the op¬ 
eration of slow sand-filters depended upon the forma¬ 
tion of a layer of sediment upon the surface, by which 
the bacteria were retained. This theory was formu¬ 
lated upon the studies of the Berlin filters in 1887 by 
Piefke, Pflugge and Proskauer, and was quite gener¬ 
ally endorsed by the majority of writers on the sub¬ 
ject. At the present time, however, it may be said 
that most of the prominent engineers of Europe look 
upon bacterial action as the principal factor. Piefke,* 
of Berlin, contends that clay particles play an im¬ 
portant part in the formation of the surface film, as¬ 
serting that as the result of experiments he found 
such a film to be more efficacious than a film com¬ 
posed largely of bacteria and algse. The most 
weighty proof that such a film is not indispensable is 
advanced by the Massachusetts State Board of 
Health in the four following propositions: 

1. This film is not necessary in intermittent filters, 
which yield as high results, apparently, when this 
layer is cracked and peeled off by the action of the 
direct rays of the sun. 

* Aphorism liber Wasserversorgung vom hygienisch technischen 
Standpunkt ausbeobachted. Zeitschrift fUr Hygiene, 1889. 





98 WA TER FILTRATION WORKS . 

2. In the studies of continuous filters of fine or 
medium sand it has been observed that in more than 
ioo instances it was possible to remove from .10 to 
.30 inch in depth of the upper layer of the filter with¬ 
out causing a diminution of efficiency. 

3. It has been observed that certain filters of 
coarse sand did not give normal bacterial results dur¬ 
ing the first months of their operation, even when 
the surface coating was thick enough to completely 
clog the filters, and yet after longer service their 
efficiency increased to the normal. 

4. Chemical analyses of the sand taken from filters 
at different depths below the surface showed an accu¬ 
mulation of organic matter, it being, in some cases, 
50 per cent, of that at the clogged surface at the 
depth of 3 inches. 

Reinisch has also stated, from his studies of the 
Altona filters, that too much significance has here¬ 
tofore been given to the surface coating. 

The studies made at the Lawrence Experiment 
Station indicate quite decisively that the removal of 
the surface layer to the depth of an inch has but a 
very slight influence upon the bacterial efficiency, in 
the filtration of the Merrimac water, and that the 
effects of such deep scraping may often be disguised 
by other considerations. With depths of more than 
an inch the effect upon the bacterial contents of the 
effluent at Lawrence was generally very marked. 

Raking over the surface to the depth of an inch, 
as compared with scraping, has not shown, under the 
conditions prevalent at Lawrence, equally good re- 


PURIFICATION BY SLOW SAND-FILTRATION . 99 

suits. A disturbance of the sand to greater depths 
than this invariably results in reduced efficiency and 
long delays in the re-establishment of normal ac¬ 
tion. The ill-effects of scraping were more ap¬ 
parent in shallow filters than in those having deep 
sand layers. This fact suggests that the steadying 
effect of deep filters is a great safeguard when the 
plant is to be operated by unskilled labor, especially 
during the winter, when ice is apt to form, and when 
shallow filters would require the most intelligent and 
careful manipulation to yield satisfactory results. 

The most satisfactory method of cleaning slow 
filters, as evolved both from American and European 
experience, is to scrape off the top surface to a depth 
of about one half to three quarters of an inch and 
then rake it over carefully and lightly to remove the 
marks of the boots of the workmen. This process is 
repeated, when necessary, until the sand layer is 
reduced to the minimum thickness allowed. The 
refilling with washed sand immediately after each 
scraping does not yield satisfactory results, as it gen¬ 
erally produces sub-surface clogging at the junction 
of the new and old sand. 

Effect of the Method of Application of Water to Inter - 
mittent Filters .—To obtain high efficiency in inter¬ 
mittent filters the water must be applied in such a 
manner as to avoid disturbing the surface of the sand 
layer. When the water is flooded over the top of 
the filter the air held in the body of the sand is forced 
to escape, and if its only outlet is through the surface 
there results a breaking of the continuity of the fil- 

j 

9 > K 

) ) * 

) 5 

> ) ) 

* i > 


100 


WATER FILTRATION WORKS. 


ter and reduced efficiency. If, however, the air is 
forced downward, and out through the underdrains, 
these ill-effects are very largely obviated. 

Effect on Bacterial Efficiency of Method of Putting 
Slozv Sand-filters in Use after Scraping. —The usual 
practice of filling filters after scraping has been to 
allow filtered water to slowly flow back into the 
underdrain of the filter and gradually rise above the 
surface of the sand. In some of the European filters 
it has been the custom to waste the first water pass¬ 
ing through after a scraping, varying the quantity 
wasted according to circumstances. It has been 
found, however, that in nearly all cases satisfactory 
results can be obtained by filling from below, allow¬ 
ing the water to stand a short while before placing 
the filter in operation, and then starting filtration at 
a rate below normal. In this manner it is found that 
a sufficiently good effluent can be obtained, in many 
cases, without wasting. With waters low in the ma¬ 
terials necessary for the production of the gelatinous 
film on the sand grains, less favorable results are ob¬ 
tainable by this method of starting; in such cases 
wasting may be necessary. 

Effect of Temperature on the Efficiency of Slozv Sand- 
filtration. —Observations at many filtration-works 
indicate that the reductions of bacterial efficiency 
which have been noted in extremely cold weather have 
been due to causes which could be removed by struc¬ 
tural and operative changes; the low temperature 
of the water not being chargeable with the reduction 
of efficiency. Open filters which have shown low 

< i 

e> i : 

I'C ( ‘ v t*1 








PURIFICATION BY SLOW SAND-FILTRA TION. 101 


efficiency in cold weather have, upon their being cov¬ 
ered over to protect them from the formation of ice, 
shown again their normal power of removing bac¬ 
teria. This has happened at Zurich, Berlin, and Koe- 
nigsberg. The filters at Altona and Hamburg and all 
the cities of England and Holland are open, and but 
little trouble has been experienced at these plants 
during winter weather. Where the winter tempera¬ 
ture is such that many days of severe cold may follow 
in succession, producing several inches, or feet, of ice, 
it will generally be economical to cover the filters. 
This subject is discussed more fully on page 120. 
The reduction of efficiency in the winter months 
may be due to the disturbance of the top surface of 
the sand during the removal of ice; to the freezing 
of the surface after scraping; or to the necessity 
of compelling certain portions of the filters to be 
cleaned more frequently than the remainder of the 
area, resulting also, perhaps, in abnormally high rates 
of filtration on the parts so cleaned. 

Conclusions .—From a careful consideration of the 
observed facts it is seen that, under favorable condi¬ 
tions, the process of slow sand-filtration may be very 
efficient for the treatment of polluted waters. It is 
also seen that some waters cannot be successfully 
treated by this process. The process is not efficient 
for the removal of coloring matter dissolved from 
leaves, roots and grass, peat and decaying organic 
matter. It is not efficient for the removal of turbid¬ 
ity caused by clay in a very finely comminuted 
condition; it is not efficient in improving the chemi- 


102 


WATER FILTRATION WORKS. 


cal quality of the water; and it is not efficient in the 
treatment of waters deficient in the organic matters 
necessary for the formation of the gelatinous film 
around the grains of sand. Further, continuous slow 
sand-filtration is not capable of purifying a water 
highly polluted with sewage and at the same time low 
in dissolved oxygen. For such waters intermittent 
filtration, or double filtration, may be necessary. In 
point of efficiency in the removal of bacteria from pol¬ 
luted waters, under proper conditions, however, this 
method of filtration takes first rank for reliability 
over all other practicable processes known to-day. 
It has passed the experimental stage, as a process, 
and is known, when properly applied under suitable 
conditions, to be safe, satisfactory and economical. 



CHAPTER IV. 

DESIGN, CONSTRUCTION AND OPERATION OF 
SLOW SAND-FILTERS. 

DESIGNING. 

Per Capita Water Consumption .—The number of 
filter-beds required to supply filtered water to a given 
population, and the size of each bed, depend princi¬ 
pally upon the per capita daily water consumption, 
and upon the character of the raw water. 

The per capita daily water consumption of the 
cities of the United States is generally higher in large 
than in small cities. This fact is one of the elements 
which makes the filtration of our large public supplies 
a matter of considerable expense, often influencing a 
city to defer improvements, in the hope that it may 
become, through more favorable conditions, better 
able to meet the expenditure at some time in the 
future. In filtration-works the annual cost of opera¬ 
tion and the original outlay for construction are gov¬ 
erned by this item, and, therefore, the necessity for 
avoiding needless waste is apparent when the purifi¬ 
cation of the water is contemplated. If a city of 
100,000 people uses 15,000,000 gallons daily, requir¬ 
ing a filter-plant costing, say $450,000 for construc- 

103 


104 


WATER FILTRATION- WORKS. 


tion and about $43,000 per year for operation, could 
get along with 10,000,000 gallons per day, the works, 
at the same rate as above, could be built for $300,000 
and could be operated for $29,000 a year. The dif¬ 
ference is apparent. It is, however, the duty of the 
engineer to solve problems on a business basis rather 
than from a strictly theoretical point of view, and the 
question of waste restriction is one of the problems 
in which business enters to a very large extent. 
While no one will dispute the advantages of 
economy, public economists differ radically in the 
means proposed for bringing about their ends. In 
large cities with long-established customs, with pecu¬ 
liar industries, with special necessities for the use of 
water and special reasons why a large amount is 
wasted, reforms can only be made gradually, and, 
as it were, at the wish of the people. If a commission 
should, in such a city, order the immediate stoppage 
of all waste and insist upon the placing of meters on 
every consumer’s supply-pipe, urging that nothing 
could be done in the way of purification of the water 
until such measures had been carried out, it would 
fail entirely in its mission, either as to reducing the 
waste or catering to the public interests by improv¬ 
ing the water. While much can be done in the re¬ 
striction of waste in cities, if the question is properly 
approached, it cannot be done in a day, and the diffi¬ 
culties of the task will increase with the magnitude 
of the city. The records of cities using meters show 
almost conclusively what can be done in this direc¬ 
tion; but when it comes to inaugurating the introduc- 


DESIGNING SLOW SAND-FILTERS. 10$ 

tion of these devices in large cities, where such action 
will affect realty investments, change the returns on 
productive property, and necessitate the expenditure 
of large sums of money for repairs and improvements 
to plumbing, there is sure to spring up opposition 
which can be overcome only with difficulty. 

It is, therefore, better to look the matter squarely 
in the face. The most practicable policy is to propor¬ 
tion the works to suit the actual water consumption 
at the time. This will provide all the water the peo¬ 
ple have become accustomed to, and will avoid the 
semblance of a water famine which would ensue if the 
reduction of the supply were suddenly brought about. 
Then, after the works are built, is the time to begin 
lessons in waste reduction. By first metering willing 
consumers, of whom there are always a great many in 
large cities, the doubtful become convinced of the 
benefits of the system, and finally enough meter- 
takers can be secured to force into line those who op¬ 
pose meters from ulterior motives. By such a pro¬ 
cedure the consumption can be gradually cut down, 
and thus, as the city grows, the reduction in per 
capita consumption will permit the original works to 
serve, perhaps, for many years before extensions be¬ 
come necessary. This policy is not wasteful of public 
funds, and is possible of enforcement in many cases. 
The attempt to cram meters down the throats of an 
unwilling public, willy-nilly, is generally productive of 
a species of mal-de-meter, so to speak, that becomes 
endemic and difficult to eradicate; the prevailing 
symptoms being a feverish excitement in councils, a 


IO 6 WATER FILTRATION WO RUTS. 

chilly reception of the measure by the press, followed 
by a feeling of intense depression on the part of the 
friends of the meter. 

The small per capita water consumption of some of 
the large European cities is often quoted as proof 
that our cities are extravagantly wasteful of water, 
but to any one who has spent considerable time in 
these cities, not in the fine hotels where rich Ameri¬ 
cans congregate to be fleeced, but in the homes 
of the middle classes and in the smaller hotels, 
the reason for the small consumption will be ap¬ 
parent on starting a search for a bath-tub or 
water-closet. They do not waste water; they do 
not use enough of it, from the American point 
of view. Manchester, a few years ago, was one 
of the favorite cases held up to wasteful Ameri¬ 
can cities as an example of what could be done 
in the matter of getting along without water; 
she is no longer useful for that purpose, because 
since the building of the sewers and the intro¬ 
duction of water-closets, wash-stands and stationary 
tubs, and numerous other conveniences that are to 
be found in every American hamlet of 3,000 people, 
the consumption is gradually climbing up to where 
it ought to be, judging from the American stand¬ 
point. It is neither practicable nor desirable to at¬ 
tempt to limit the use of water in our large cities 
to such low figures as are quoted for some of the 
foreign cities, as we have different conditions of 
national temperament and municipal and govern¬ 
mental administration. A great deal can be done, 


DESIGNING SLOW SAND-FILTERS. 10 7 

however, in the detection of useless waste, by in¬ 
spection, or other means, and offenders should be 
brought in line, so as to keep the consumption down 
to the lowest practicable limit, in order to save ex¬ 
pense in construction and in the operation of the 
works. 

Number of Filter-beds Required, and Excess Area 
to Be Provided .—Having decided upon the per capita 
water consumption, the most advisable rate of fil¬ 
tration, in consideration of the character of the 
water and the sand, the proportioning of the number 
of beds and the size of each depends upon the 
amount of area that must be provided in excess, to 
permit of the periodical cleaning of the beds. This 
excess area varies greatly in the extant works, rang¬ 
ing from 5 per cent, to about 20 per cent, of the 
total area, and in some of the smaller ones being 
100 per cent. It is not necessary, usually, to propor¬ 
tion the works for a much larger population than 
is resident in the city when they are completed, 
because the plant will be capable of extension at a 
cost probably not much higher in rate than the cost 
of the original works, with the possibility of defer¬ 
ring extensions if it is feasible to reduce the waste 
in the city. 

For waters carrying a good deal of suspended 
matter, or particularly rich in algae growth, the re¬ 
quired proportion of excess area will be greater than 
for clear waters, because in the former cases the beds 
will require frequent cleaning; under such condi¬ 
tions, with proper preliminary treatment by sedi- 


io8 


WATER FILTRATION WORK'S. 


mentation or other methods of clarification, it is 
seldom that the beds will require cleaning oftener 
than once a week, when operating at ordinary rates; 
while with clear waters it is seldom that the beds 
will require cleaning as often as once in two weeks. 
In most of the existing works the average period 
between cleanings is about a month. 

After deciding upon the allowable maximum rate 
of filtration, the proper size and number of beds may 
be determined when the maximum daily draft on the 
filters is known. The water consumption will fluctu¬ 
ate with the time of day, with the days of the week, 
and the seasons of the year. The maximum to be 
expected should not exceed the average daily 
draft by more than from 50 to 60 per cent., and, 
therefore, unless there are storage reservoirs of am¬ 
ple capacity in the distribution system, the beds 
should be proportioned to deliver in 24 hours 1.5 to 
1.6 times the average daily draft, in order that the 
maximum rate of filtration may not be exceeded. A 
reservoir sufficiently large to balance the hourly fluc¬ 
tuations in draft should also be provided. A discus¬ 
sion of the proper amount of storage to meet this 
requirement will be found in chapter VIII. 

If the distribution or storage reservoirs are large 
enough to balance the daily fluctuations of draft, the 
beds may, of course, be designed'for average draft 
instead of maximum. 

As has already been discussed on pp. 93 to 96, the 
increase, within reasonable determinate limits, of the 
rate of filtration of slow sand-filters operating nor- 


DESIGNING SLOW SAND-FILTERS. IO 9 

mally at fairly slow rates may occasionally be per¬ 
missible for short periods of time, depending upon 
the relative pollution of the water, and other factors. 
Advantage may sometimes be taken of this to design 
the filters for the average draft of water, providing a 
small filtered-water reservoir to balance the sudden 
changes in rate of draft, and depending upon the 
flexibility of the filters to meet the daily or seasonal 
variations. 

The total necessary effective area for the filter- 
beds, including the surplus area, to be provided to 
permit of the periodical cleaning of the filters as they 
become clogged and still not work the remaining 
beds beyond the prescribed limits, may be found from 
the following formula: 

cn* v 

/ + c \ 
cri * J 
~ 7+~c' 

A — total necessary area, including reserve, in acres. 
Q — total quantity of water to be filtered daily in 
million gallons. 

r = rate of filtration in million gallons per acre per 
day. 

n = number of filter-beds, including reserve beds. 


^ = jl 1 + 


1 + 


71 — I 


* The expression ;— will generally be fractional, but in the 

« PNc 

formula use the nearest integer as follows : If the expression 
equals or is less than 1, 2, 3, 4, etc., take as its value in the 
formula o, 1, 2, 3 etc., respectively. If it is greater than 1, 2, 3, 
4, etc., take as its value 1, 2, 3, 4, etc., respectively. 







IIO 


WATER FILTRATION WORKS . 


p — ordinary minimum number of days of service 
between cleaning. 

c — number of days each filter is out of service while 
draining, cleaning, and refilling. 

The following illustrations will serve to show the 
relative effects on the size of the beds, of different 
assumptions regarding the operation of the works, 
and will point out the economies which may be ef¬ 
fected in designing and operating a plant. 

Suppose a city uses 100,000,000 gallons of water 
daily, and the filters are to operate at the maxi¬ 
mum rate of 5,000,000 gallons per acre daily. 
The plant consists of 20 beds, the average period be¬ 
tween cleanings is six days, and each filter is out of 
service three days for cleaning, resting, and refilling. 

1. The area of each bed would be 1.5461 acres, 
requiring a total area of 30.92 acres. 

2. If the lapse of time between cleanings were 
thirty days the area of each bed would be i.m acres, 
and the total area 22.22 acres. 

3. If in the first instance the beds were out of ser¬ 
vice only two days instead of three, the area of each 
would be 1.33 acre, and the total area 26.6 acres. 

In the second case the beds were designed for 
monthly cleanings, and 2 beds would be in clean¬ 
ing, while 18 would be in service. If now a period 
of bad water were to come on, and the beds required 
cleaning every six days, it would be necessary to 
have 7 beds in cleaning, and 13 beds, with an area 
of 14.55 acres only, would be in service. For these 
13 beds to deliver the requisite 100,000,000 gallons 


DESIGNING SLOW SAND-FILTERS. 


Ill 


daily the rate of filtration would have to be increased 
to about 6.92 million gallons per acre per day, or to 
a rate about 38 per cent, above the normal rate. 
The effect of changing the rate by this amount 
might not be so dangerous as to preclude its occa¬ 
sional occurrence if special precautions were taken 
during these periods to insure as great efficiency as 
possible. It would, therefore, under the conditions 
assumed, not be economical to proportion the beds 
upon the basis of weekly cleanings, as that assump¬ 
tion would necessarily increase the cost of the plant 
by about 60 per cent. On the other hand, no 
economy would result, in this case, in designing the 
beds for a period of as long as forty-five days between 
scrapings, because there would still be 2 beds in 
cleaning, and the proportion of reserve area would 
be the same, unless the number of beds were less 
than 17. 

Now as to the effect of changing the number of 
beds, still assuming the same quantities for con¬ 
sumption, rate of filtration, a thirty-day period be¬ 
tween scrapings and three-day periods of rest: 

Supposing 11 beds were built; the area of each 
would be 2 acres, and the total area 22 acres, thus 
requiring 0.22 acre less than if 20 beds 'had been 
built. Assuming that the cost of filtering materials, 
roofing and flooring are the same per square foot of 
area for filters of all sizes, an assumption not far from 
the truth, there would be a saving, in using 11 beds, 
of 9 division walls between filters, 9 inlet wells with 
regulating apparatus, 9 outlet wells, 0.22 acre of fil- 


112 


WA TER FILTRATION WORKS . 


tering materials, roofing and flooring, and a small 
saving in the cost of underdrainage. 

The increased cost and disadvantages, from the 
use of ii beds, would result from a slightly greater 
inconvenience in handling the sand in scraping and 
refilling; and, in open filters, where ice of consider¬ 
able thickness is apt to form, additional difficulties 
in scraping, and in disposing of the ice. 

It is evident, however, that economy of construc¬ 
tion favors large beds. In any case it is necessary 
to decide, first, the maximum rate of filtration to be 
allowed and then to determine the corresponding 
number of beds, regard being had to the period be¬ 
tween scrapings that will make the total area the 
least while insuring that the allowable maximum 
rate on the beds in use will not be much exceeded if 
the period between scrapings is occasionally re¬ 
duced to six days. The maximum practicable size 
for filter-beds has not been definitely determined. 
The largest in use are the uncovered beds at Ham¬ 
burg, which have an area of 1.88 acre each, and 
have given satisfactory results. Most of the beds of 
the other European filters are from .5 to 1.5 acres in 
area each. Frequently local prices of land, of labor 
and of materials may have an important influence 
in deciding the size of the beds. It would hardly be 
necessary in any case to make the beds larger in 
area than 2 acres each, as even in very large plants 
no great economy would result from using larger 
sizes. 

In the examples which have just been discussed, 


DESIGNING SLOW SAND-FILTERS. 113 

if the maximum rate had been fixed at 7.5 million 
gallons per acre daily, it would have been found 
more economical to use 16 beds and a period 
of service of forty-five days between scrapings. 
In this case the 15 beds in service would ordi¬ 
narily deliver the prescribed quantity at the rate 
of 5,000,000 gallons per acre daily, and the total 
area required would have been 21.33 acres; 0.89 
acre less than with 20 beds designed for thirty-day 
periods, and 0.66 acre less than for 11 beds also de¬ 
signed for thirty-day periods. If a different length 
of time is assumed for the filter to be out of service 
the resulting proportion of reserve area will also be 
slightly changed. 

Location and Grouping of Beds .—After having de¬ 
termined the proper area and number of beds, the 
grouping of the beds into an economical design will 
be influenced by the shape of the available tract of 
land, its topographical features, and the judgment 
of the designer. The points to be borne in mind are: 
A sufficient area must be reserved for the washing 
and storing of the sand during cold weather, when 
washing* would be attended with considerable diffi¬ 
culty and expense; and, in case the beds are not cov¬ 
ered, for sufficient space for storing ice cut to per¬ 
mit cleaning; to allow of sufficient room for the 
location of the various pipes below the ground, and 
the tramways above the ground for the handling of 
the materials; for the convenient placing of the filters 
relative to the sand-court so as to make the average 
distance that the sand must be conveyed as short as 


WATER FILTRATION WORKS . 


114 


а , INTAKE FROM LAKE. 

б, fore-bays 

C, PUMPING MACHINERY FOR DELIVERING 
WATER ON FILTERS. 

d , 34 SAND FILTERS. 

e , 4 FILTERED-WATER RESERVOIRS. 

' /, PUMPING STATIONS FOR SENDING 

FILTERED WATER TO CITY. 

(/, SAND WASHING MACHINERY. 

Zi,, ENGINEER’S OFFICE, 
t, LABORERS' LUNCH AND WAITING HALL. 
Jc , RESIDENCES and offices of the 
OFFICERS OF THE WORKS. 





100 

SCALE OF METERS 




200 
■ . I 






S# 


.*v*V w—v 

mi 

•Vv'A'j 

.'■Y. 

iv^Vs 


: v> r?*-:.'- 

ip 



I 

1 9 




Fig. 5.—Arrangement of the Lake Muggel Filter Plant 

Berlin, Germany. 

















































DESIGNING SLOW SAND-FILTERS. 


115 


possible, and the proper placing of the dear-water 
reservoir relative to the filters so as to make the 
length of piping a minimum. The arrangement of 
the Lake Miiggel works at Berlin is shown in Fig. 5. 

Shape of Filter-beds .—Filters are usually made 
rectangular in plan wken the topography of the land 
does not require some other shape. Circular or 
polygonal shapes are rarely used when the rectangu¬ 
lar shape is possible, although in very small covered 
filters the circular form is quite advantageous. The 
principal arguments for the circular shape are that 
with it the cost of surrounding walls is a minimum 
for a given area, and the area of contact between the 
side-walls and the sand is a minimum, thus re¬ 
ducing the danger of unfiltered water passing down 
between the sand and walls also to a minimum. A 
typical plan of one of the Berlin filters (Lake Mug- 
gel) is shown in Fig. 6. The most economical shape 
for a rectangular filter-basin, if not subdivided, is the 
square. If divided into several basins the economi¬ 
cal dimensions may be obtained from the following 
formulas, in which it is assumed that the dividing 
walls cost about the same per foot run as the side- 
walls. 

If the basins are all in one row, side by side, the 

fi 1 

length of the short side, x =- y } in which y is 

the length of the long side and n the number of fil¬ 
ters. If the filters are placed in two rows, back to 
back, and side by side, in the row, the formula be- 



'DRAIN EOBJiAKOTG WATER OEF.TWE SURFACE OF FILTER 


116 


WATER FILTRATION WORK'S, 



Fig. 6.—Plan ok Berlin (Muggel) Filter-bed. 


DRAIN FOR TAKING WATER OFF THE SURFACE OF FILTER 































CONSTRUCTION OF SLOW SAND-FILTERS. 11? 

2(ji j 2 \ 

. comes, ^ = ———, if there are the same number of 

j u 

beds in each row. 

Depth of Filters .—The depth should be sufficient 
to provide for the filtering- materials and the superin¬ 
cumbent water; it will generally be about 10 feet, 
varying a foot or two each way from this in special 
cases, depending upon the fineness of the filter-sand, 
the character of the water and the economies of 
design. 


CONSTRUCTION. 

Preparation of Site .—Where the ground-water 
level is higher than the bottoms of the proposed fil¬ 
ters, the site should be drained by a system of pipes, 
laid with open joints, and surrounded with gravel, so 
that after the filters are completed there can be no 
upward pressure on their bottoms. The drains 
should discharge at an outfall, or into a sump, or 
well, from whic'h the water may be pumped. The 
site of the Hamburg filters is underdrained in this 
way, the sub-soil water being pumped from a well 
and discharged into the river. 

Side Slopes and Bottoms .—Open filters are fre¬ 
quently built with sloping side-walls, formed in ex¬ 
cavation or by embankment, rather than with verti¬ 
cal retaining walls. The side slopes are usually 1 
to 2 or 1 to 3, and are protected in various ways. 
Generally a layer of well-packed clay provides for 
water-tightness, the surface being protected by a 
paving of brick, stone, or concrete. The Hamburg 



11 8 WATER FILTRATION WORKS. 

filters are excavated with side slopes of I to 2. The 
bottoms and slopes are covered with puddled clay. 
The bottom is paved with a floor of bricks laid on 
their sides, and the slopes with bricks set on edge; in 
both cases laid in cement mortar. In using this 
method of lining very hard impervious bricks are de¬ 
sirable. In the zone where there is danger of ice 
forming and adhering to the sides, every precaution 
should be taken to make the paving impervious and 
able to resist frost and abrasion. Open beds with 
sloping side-walls present the advantage that they 
are not so apt to be damaged with frost and ice as are 
those with vertical walls. The beds with sloping sides 
are said, however, to be the more difficult to keep 
water-tight. All square corners should be avoided 
in the construction of beds with sloping side-walls, 
as there is great danger of the formation of cracks 
along the angles, which would allow the water to per¬ 
colate to the underdrains without being properly fil¬ 
tered. The relative costs of open beds with sloping 
and those with vertical side-walls will depend upon 
circumstances. Usually beds with sloping sides will 
be the cheaper, but if land is very expensive it might 
be possible that those with vertical walls would be 
preferable. 

When the ground upon which the filters are to be 
built is compressible and yielding, many difficulties 
may be encountered in holding the excavation and 
the walls. In such cases foundation piles under the 
walls and piers, and sheet piles around the edges of 
the excavation, or, pediaps, the construction of the 


COATS TR UCTION OF SLOW SA A T D-FIL TERS. I 19 

side-walls in trenches, followed by the excavation of 
the interior space, or the dividing of the excavation 
into different sections may be necessary. 

Precautions to Prevent Water Passing to the Under- 
drains in an Unfiltered State. —The greatest care 
should be taken to secure perfectly water-tight work¬ 
manship, so that there may be no possibility of un¬ 
filtered ground-water finding its way up through the 
bottom and into the underdrains. 

Sharp salient and re-entrant angles of all piers, 
buttresses and side-walls should be rounded off to 
insure better contact between the sand and the ma¬ 
sonry, to preclude the danger of the water following 
such angles to the bottom of the filter without being 
properly purified. In order to prevent the unfiltered 
water from creeping between the side-walls and sand 
it would be well, in concrete construction, to batter 
the walls, piers and buttresses, from the bottom to 
above the level of the filtering materials, so that the 
settling of the sand under the action of the water 
would tend to make the contact closer the longer the 
filter is in use. In the Albany filters Mr. Hazen in¬ 
troduced ledges around the faces of the walls and 
piers, below the surface of the sand, formed by steps 
or offsets in the brick work. Mr. Rudolph Hering 
has suggested the sanding of the concrete surface be¬ 
fore the mortar has set. 

Effects of Hot Sun on Open Filters. —Serious leaks 
due to cracking of the underlying clay-puddle are apt 
to occur in open beds, when they are exposed to the 
hot sun for several days with the water drawn off 


120 


WATER FILTRATION WORKS. 


and the filtering materials removed. Under such 
conditions there may also occur a buckling of 
the floor and side-walls, or a formation of cracks, 
resulting in decreased efficiency of the filters. These 
dangers are entirely avoided by covering over the 
beds with a roof, carried on piers, and overlaid with 
a few feet of earth. In cold climates this covering 
is doubly necessary to prevent the formation of ice 
of considerable thickness upon the surface of the 
water, the removal of which, by disturbing the top of 
the sand and by pre-requiring the greater part of the 
water to be filtered upon the limited area that can 
be kept properly scraped, may reduce the efficiency 
very greatly. 

Covering Filters .—It cannot be said that there are 
any advantages to be gained from covering filters, 
excepting to avoid the difficulties inherent to keep¬ 
ing the filters operating properly during cold 
weather, and to prevent the growths of algae, which 
produce rapid surface clogging on the filters in sum¬ 
mer weather. To prevent the latter trouble, a light, 
inexpensive trussed roof would suffice, as its only ob¬ 
ject would be to exclude light. Covered and uncov¬ 
ered filters, other things being equal, yield equally 
good results, when properly operated. 

Open filters are more easily cleaned than those 
with covers, and have the advantage of presenting 
an unbroken surface for the filtration of the water. 
Covered filters have many columns, piers, buttresses, 
etc., which pass through the filtering materials, and 
around which it is difficult to place the sand with the 


CONSTRUCTION OF SLOW SAND-FILTERS. 121 


same degree of compactness as in other portions of 
the filter. On account of the space taken up by 
these piers and buttresses additional area is required 
to compensate therefor. It is also said that for some 
kinds of water it is difficult to secure sufficient venti¬ 
lation in covered filters during summer. This, how¬ 
ever, seems to be a small point. 

Generally speaking, therefore, covering will be 
necessary in climates where long periods of severe 
cold are likely to occur in the winter, or where algae 
growths would seriously interfere with the economic 
operation of the plant in the summer. In cities 
where the question becomes an economic one, a study 
s'hould be made of the number of successive days of 
freezing weather, the degree of cold during these 
spells and the lengths of the periods of intervening 
thaws. The formation of ice on the water will not, 
per se, affect the efficiency of filtration. If the ice 
does not last longer than the period during which the 
filters can be safely operated between cleanings, it 
need not be considered as a factor in the question of 
providing covers. Since covered filters cost from 50 
to 100 per cent, more than the open type, it may, in 
some cases, be cheaper to provide more area of open 
filters than to cover those actually required, if by 
that means the plant can be operated a sufficiently 
long time to allow the ice to melt or be safely re¬ 
moved from part of the area before scrapings are 
necessary. In rather mild climates a trussed roof, 
similar to that over the Koenigsberg filters, might 
afford sufficient protection, or some of the beds 


122 


WATER FILTRATION WORKS. 


might be covered and some left uncovered, as at 
Stralsunder. 

Another combination which might be advantage¬ 
ous in climates where ice would give trouble, would 
be to provide a certain proportion of the required 
filter capacity in open slow filters, and the remainder 
in rapid filters with a comparatively low’ rate, say 
100,000,000 gallons per acre per day. Then during 
very cold weather the slow filters could be operated 



at a slow rate, perhaps half of the summer rate, so as 
to postpone the times of scrapings, and the rapid 
filters could be operated somewhat more rapidly 
than at the summer rate. This presupposes that the 
water is of a character to be successfully treated with 
rapid filters. The flexibility of rapid filters, within 
pretty wide limits, as noted in chapter III., makes 
such a combination as this quite practical, and in 
some cases may permit the building of open slow 
sand-filters, the whole plant being very much less 






























CONSTRUCTION OF SLOW SAND-FILTERS. 123 

expensive than one consisting entirely of covered 
slow sand-filters, while at the same time being equally 
efficient. During the winter time, the relative pol¬ 
lution of most streams is lower than in summer, be¬ 
cause the polluting matter is retained longer on the 
surface of the ground, and the stream flow is also 



Fig. 8.—Masonry Groined Arches with Arch Ribs. 


generally greater than during the summer months. 
Thus in the summer the main reliance would be upon 
the slow sand-filters, and during the winter upon the 
rapid sand-filters. 

In very cold climates the cost of removing the ice 
is a significant part of the cost of operation of open 








































124 


WATER FILTRATION WORKS. 


filters. The tendency in the German works is tow¬ 
ard covered filters, while in England and Holland 
the filters are almost without exception uncovered. 

Groined arches (Fig. 7, 8 and 9), springing from 
the tops of columns, are generally used for covering 
filter-beds, because of the ease with which they may 



be constructed of brick masonry or concrete. An 
interior view of the Ashland, Wis., covered slow sand- 
filter plant, designed by Wm. Wheeler, C.E., is 
given in Plate V. The roof over this filter is the first 
application in the United States of groined arch con¬ 
struction for a filter cover. 




























Plate V.—Interior View of Ashland, Wis., Covered Filters. First Adaptation 
in the United States of the Groined Arch as a Filter Roof. 

































CONSTRUCTION OF SLOW SAND-FILTERS. 1 2*] 

The average thickness of the groined concrete 
arches covering the Albany filters is about 7 inches, 
the thickness at the crown being 6 inches. 

The new Berlin filters have covers of a unique de¬ 
sign. The roof is a series of domes, supported on 
piers (Figs. 8 and io). The domes were constructed 



Fig. io. —Domed Covering with Arch Ribs. 

by springing arch rings from the tops of the piers, 
on the sides and diagonals of each panel, and then 
filling in the space between the rings with the shell 
of a dome, the brick being put in place by hand, 
without the use of centres. The work is beautifully 
done and is very effective, although much more ex¬ 
pensive than concrete groined arches would have 
been. They have a way of doing things in Europe, 
particularly in Germany, in the building of public 
works, which might well be emulated by American 
























































128 


WATER FILTRATION WO RES. 


cities, to a certain extent, at least. In our average 
American town the policy is usually to be over-or¬ 
nate in structures showing above ground, and to be 
over-economical in the execution of works which are 
out of sight. Very often, however, this policy is not 
truly economical. In works pertaining to public sani¬ 
tation nothing can be too good that will conduce to 
the greater care and attention which attractive sur- 



Fig. ii.—Cylindrical Arches. 


roundings will naturally beget. Nothing is more con¬ 
ducive to good maintenance than appropriate con¬ 
struction and well-built structures. For this reason, 
in filter plants, the effort should be made to have the 
interior finish of the walls, piers and arches properly 
carried out, and the gate-houses, entrances and other 
works above ground architecturally presentable. 
Few engineers are skilful enough designers to be 
trusted with the treatment of the architectural fea¬ 
tures. The countless monstrosities in the shape of 
pumping stations, etc., that are to be seen in our 
large cities bear witness to the folly of entrusting 
















CONSTRUCTION OF SLOW SAND-FILTERS. 1 29 

such designs to men educated highly, no doubt, in 
the uses for which the structures are built, but incom¬ 
petent architecturally and artistically. 

Domed constructions, cylindrical arches (Fig. 11) 
or composite roofs of steel and concrete may be used 
instead of groined arches, if desirable. An eco¬ 
nomical form of roof is one composed of flat domes 
resting on the tops of piers (Figs. 12 and 13) similar 



to the Berlin roof, above described, but made of con¬ 
crete and expanded metal. The cost of making the 
centering for this form is a trifle more than for 
groined arches, but the saving in concrete is very 
considerable. A view of the centering for the groined 
arches forming the roof of the Somersworth, N. H., 
filter is given in Plate VI. 

By the use of the domed construction with ex¬ 
panded metal, properly placed, the average thick¬ 
ness can be reduced considerably below that required 
for groined arches. The author has built a circular 
reservoir for spring water, now in service, covered 













































130 WATER FILTRATION WORKS . 

with a concrete and expanded-metal dome, of a span 
of 16 feet, rise of 2 feet, and average thickness of 
5 inches, with a covering of 2 feet of earth. 
The earth covering was dumped on it from wagons. 
He has also built two other domes, in a similar man- 



Fig. 13. —Concrete Domed Construction. 


ner, having spans of 20 feet, rise of 3 feet and aver¬ 
age thickness of 5 inches. 

Drainage of Roof .—The water falling on the roofs 
of filters may be allowed to drain into the filters 
through the roof, in pipes carried down through the 
piers and discharging above the level of the sand. 
The top ends of these drains should be covered in 
some way so as to prevent the entrance of dirt, and 
should provide free exit for the water, so as to pre¬ 
vent injury to the work by the action of frost. 

The roof should be covered with coarse sand, or 


































Plate VI. —Somersworth, N. H., Covered Filters. Bird’s-eye View of Cen¬ 
tering for Groined Arches. 







CONSTRUCTION OF SLOW SAND-FILTERS. 133 

gravel, to facilitate drainage, and on top of the 
gravel about two or three feet of earth should be 
spread to keep out the cold. The top six inches of 
filling should be top-soil, which should be fertilized 
and seeded with grass, while the slopes of terraces 
or banks should be sodded. The treatment of the 
tops of covered filters offers opportunities for the 
display of taste in landscape work. 

Ventilation .—Much more provision should be 
made for ventilation and lighting than is usual in 
reservoir construction, as the operations of cleaning 
and refilling filters will occur quite frequently and 
can only be done effectively in good light. 

In the centre of alternate panels in the roof man¬ 
holes should be built to provide for ventila¬ 
tion and light. These should extend from the roof 
to the top of the earth covering, and should be about 
two feet in diameter at the top and slightly larger 
at the bottom. Each should be provided with a 
cover which could be removed if necessary. A con¬ 
venient and satisfactory arrangement is to have a 
double cover, the lower one being wire-glass and the 
upper one of metal treated with a preservative coat- 
ing. 

In large plants it is desirable, if not always neces¬ 
sary, to install an electric-lighting plant, with arc 
lights for the sand-courts, roads, etc., and incandes¬ 
cent lights placed in the gate-houses, and distributed 
through the basins of covered filters. 

There is no reason why the roof need be much 
above the highest water-level, though sufficient 


134 WATER FILTRATION WORKS. 

head-room should be provided, of course, for the 
convenience of the workmen in cleaning. The actual 
height will depend upon the depth of water allowed 
upon the filter surface, the limiting filtration head 
and special features of the regulating apparatus and 
conduit leading to the filtered-water reservoir. 

Tramways for Sand Haulage .—In nearly all the 
large slow sand-filter plants now in operation it is the 
general practice to provide tramways for transport¬ 
ing the sand removed from the beds to and from the 
sand washers. It will not be long, however, before 
some radical changes will be effected in the methods 
of cleaning slow sand-filters, having for their object 
the reducing of the amount of hand labor involved in 
the process as now practised. When tramways are 
used it is convenient to provide branches from the 
main tracks, one running into each covered filter and 
sloping down to the level of the sand surface, so that 
the cars can be taken in and out of the filters. The 
track should be supported between two rows of piers 
and extend generally to about the centre of the filter. 
Over the track the roof is usually a cylindrical arch, 
its axis sloping with the track so as to provide suffi¬ 
cient head-room. 

For open filters portable tracks are used with suc¬ 
cess. 

Bottoms .—Inverted groined arches, Fig. 14, make 
the best form of bottom for slow sand-filters, because 
this form is economical, furthers the proper distribu¬ 
tion of the load on the columns carrying the roof, 
gives a strong section and provides valleys in which 


Plate VII.—Somersworth, N. H., Covered Filters During Construction. 



CO 

U1 










CONSTRUCTION OF SLOW SAND-FILTERS. 137 




JX’RTK CQVERINi 


pLCONCRETE^= 
GROINED ARCHES 


WATER LEVEL 






'S A N D RU^ 

TRACKS 


SAND 


iOHCREIfc 


7rw;vw, 







^CONCRETE - ^^ 
r GROINED ARCHES 

— 

WATER LEVEL ^ 


: 


— 

r 

W.WV.'H 






iKTTT' 


— - 

^= f= " 

^’*•^1 A- li'. L: j.\ li'lv.'; liV'' 


{ •v.Y.y. •. ■. v.\ s Y|\v •»i '• 

""^^gravel" 


r. .-(iru, « .V-;, 1 1; 

‘••’SAND RLfN N * 
TRACKS 


/GRAVEL 


UNDERDRAIN '^L'J^MAIN UNDERDRAIN CONCRETE^ 


SECTION A-B 

mrmrrrrrrrrrr7> 


CONCRETE VAULT 


SECTION C-D 


SCALE OF FEET 



0 10 20 30 40 


Fig. 14.—Typical Plan and Sections of Covered Slow 

Sand-filter. 




















































































































































138 WATER FILTRATION WORKS. 

the underdrains may be laid. Slow sand-filter floors 
should never be horizontal planes, but should be 
broken into ridges and valleys inclining towards 
the underdrains so as to remove the water as 



Fig. 15.—Plan of Filter-bed, Zurich, Switzerland. 

fast as it is filtered. The manner of accomplish¬ 
ing this in the Zurich filters is shown in Fig. 
15. If allowed to stand in the gravel the water will 
gradually deteriorate in quality, to a greater or lesser 
degree. The best practice, in regard to the under¬ 
drains for collecting the water after it has passed 
through the sand and gravel, is to use small vitrified 
pipes for the lateral drains, placing them upon the 


















CONSTRUCTION OF SLOW SAND-FILTERS. 139 

filter floor, and form the main collector in the con¬ 
crete bottom of the filter. This main collector should 
have a semi-circular invert and straight vertical side- 
walls and should be covered with slabs of concrete 
or stone. 

This method is better than using pipe, built into 
the concrete, for the main collector, because during 
the construction of the basins, mortar, dirt and other 
debris is likely to get into the main underdrain, and 
its cleaning later may be a difficult matter. With 
the open drain, 'however, the debris can be easily 
removed. 

Underdrciins .—The sizes of the underdrains depend 
upon the area of the bed, the distance between the 
collectors and the amount of water to be fil¬ 
tered in a given time. In proportioning the sizes, 
ample allowance should be made on the side of 
safety, so that the frictional resistances may not 
cause unequal rates of filtration in different parts of 
the beds. As the cost of the underdrains is a very 
insignificant part of the cost of filter-beds, it is bad 
practice to attempt to keep the sizes down to the 
danger limit, to save a few hundred dollars, at the 
risk of lessening the efficiency of the filters. I would 
suggest that if the sizes are proportioned so that the 
total frictional resistance, when filtering at the maxi¬ 
mum rate, from the outlet to the most distant point 
is kept down to about .01 to .02 foot, no trouble 
will be experienced. 

Great care should be taken in placing the under¬ 
drains, if of pipes, to leave enough space open at the 


140 


WATER FILTRATION WORA'S. 


joints to permit the water to enter without requiring 
too great velocity head. 

The conversion diagrams (Figs. 16, 17 and 18) will 


GALLONS PER SECOND. 



Fig. 16.—Conversion Diagram. 

Gallons per day into cubic feet per second and per minute, and 

gallons per second. 

be of service in estimating the quantities of water that 
will be discharged by the underdrains and collectors. 

For convenience in proportioning the sizes of pipe 
underdrains, Fig. 19, based on Kutter’s Formula, 
with n = .013, has been prepared. Knowing the 
quantity of water to be filtered, and the allowable 
loss of head, the sizes and slopes can readily be found. 
In place of using pipes for underdrains some works 



















































































































































































CONSTRUCTION OF SLOW SAND-FILTERS. I4 1 


have floors made of two layers of ordinary bricks, 
the bottom bricks resting on edge, a little distance 


g VERTICAL DEPTH IN FEET**' 



apart, and the top layer lying flat upon them to form 
the floor for the filtering materials. In other places 



































































































































































142 


WATER FILTRATION WORKS 


special hollow bricks are used for the purpose. The 
form of bricks used at Zurich is shown in Fig. 20. 
There is no special advantage to be gained by this 

MILLION GALLONS PER ACRE PER DAY. 



Fig. 18.—Conversion Diagram. 

Million gallons per acre per day for different areas into cubic 

feet per second. 

form of construction, and its cost is considerably in 
excess of the more simple expedient of using vitri¬ 
fied pipes and properly graded and placed gravel 
layers. 

Gravel Layers .—To provide free passage laterally 
to the underdrains it is the custom to cover the floor 




















































































































































































































CONSTRUCTION OF SLOW SAND-FILTERS. 143 


with layers of gravel or broken stone of sufficient 
thickness to permit free passage of the water without 
consuming too much friction head. The resistance to 



Fig. 19.—Diagram Showing Frictional Loss of Head in 

Pipes. 


the motion of the water depends upon the size of the 
particles of the gravel, the rate at which the water is 
passed through the gravel, the temperature of the 

























































































































































144 WATER FILTRATION WO RUTS. 

water, and the thickness of the gravel layer. In Fig. 
21 the data given in the report of the Massachusetts 
State Board of Health for 1892 are arranged in such 
a manner that the loss of head in a gravel layer one 
foot thick can be taken by inspection, for various 
sizes of gravel and distances that the water must 



Fig. 20.—Hollow Floor, Zurich Filters. 


travel to reach the underdrains, for a rate of filtration 
of one million gallons per acre per day. For other 
thicknesses of gravel the rate will vary inversely as 
the thickness, and for other rates of filtration di¬ 
rectly as the rate. 

The gravel should be placed in the filters in con¬ 
tinuous layers, the particles of each layer being a 





















CONSTRUCTION OF SLOW SAND-FILTERS. 145 

little smaller than those of the layer below, to pre¬ 
vent the filtering sand from being washed into the 
drains. The coarse gravel, or broken stone, bed is 
to be considered only as serving the purpose of per¬ 
mitting the more or less free movement of the water 
to the underdrains. The superimposed thin layers of 
gravel of decreasing sizes are to support the sand 



*. RAJB OF FILTRATION, 1 000000 GALLONS PER ACRE DAILY: FOR OTHER RATES 

THE LOSS OF HEAD WILL VARY DIRECTLY AS THE R/WTE. 

Fig. 21.—Diagram Showing Head of Water Consumed in 
Passing Horizontally Through Gravel Layers. 

and prevent it from being carried into the under¬ 
drains by the sinking of the water. 

These layers need not be thick, but they should 
be of screened gravel, and each layer should be con¬ 
tinuous over the one below it. When properly placed 
and graded as to sizes, experience has shown that 
there is very little movement of the particles, and 
layers li to 2 inches thick, depending upon the size 
of the particles, have been found to be in peifect con¬ 
dition after several years of service. No difficulty 
will be experienced if care is taken that the particles 




































































146 


WATER FILTRATION WORRTS. 


in each layer are not more than three or four times 
as large as the particles in the superimposed layer. 
An interior view of the Somersworth, N. H., slow 
sand-filters, taken when the underdrains and gravel 
layers were being placed in position, is given in Plate 


VIII. 


The influence of the size of the particles and the 
thickness of the layers will be felt in the head used 
up in the passage of the water to the underdrains. 
The smaller the gravel and the thinner the layer the 
greater the head necessary to pass a given quantity 
of water in a given time. This may result, with poor 
designing, in the parts of the filters remote from 
the drains passing the water at a slower rate than 
parts over the drains, a condition which should be 
avoided as much as possible. Since the thickness of 
the gravel layer must be deeper the greater the dis¬ 
tance between the underdrains, there can be found 
an economical depth of gravel when the size of its 
particles, its cost, the rate at which the water is to be 
delivered, and the allowable loss of head are known. 

Filtering-sand .—The velocity with which water 
will pass through sand layers of different effective 
sizes, at different temperatures, and under different 
heads, has been the subject of experiment by the 
Massachusetts State Board of Health at different 
times. The first experiments were summarized in 
the report for 1892. These results were expressed 
by the formula: 


v — 



hit Fahr. 


60 


. + io° 



Plate VIII.— Interior View of Somersworth, N. H., Covered Filters. Underdrains 

and Gravel being placed in position 147 










CONSTRUCTION OF SLOW SAND-FILTERS. 149 

v = tht velocity of the water in a solid column of the 
same area as that of the sand, in meters, daily, 
or approximately, in million gallons per acre 
daily. 

c = a constant; its value for clean sands is about 
1,000, and for filters that have been some time 
in service it is about 800. 

ff = the effective size of the sand grain in millimeters. 
/i = the loss of head due to passing through the sand 
at the given rate. 

/ = the thickness of the sand layer. 
t — the temperature of the water in degrees Fahren¬ 
heit. 

The formula only applies when the pores of the 
sand are entirely filled with water, when the sand is 
well compacted, and when there is no clogging of 
the pores. It is also applicable only in the case of 
sands from 0.10 to 3.00 mm. in effective size, and 
with uniformity coefficients lower than 5. 

From this formula the loss of head, h, can readily 
be found if the rate of filtration, the effective size of 
the sand and the depth of the filtering materials are 
given. 

Depth of Sand .—The effect of the size of the sand 
grain, uniformity coefficient, depth of the sand layer 
and the rate of filtration, on the efficiency of the pro¬ 
cess of slow sand-filtration were fully discussed in 
Chapter III. 

The usual depth of sand in the European filters 
is from 2 to 3 feet, but in most of them, however, 
the gravel layers under the sand are very much 


150 WATER FILTRATION WORKS. 

thicker than necessary. It is advisable to make the 
gravel layers as thin as would be safe, in order that 
the total depth of the filter may not be unduly in¬ 
creased. The proper depth for the sand will vary ac¬ 
cording to its character and the character of the wa¬ 
ter. Very coarse sands require thick-beds, while very 
fine sands do not require so great a thickness. The 
best thickness can only be determined from a study 
of the sand and the results that must be obtained. 
Generally, with ordinary sands, such as would be 
called good mortar sands, and ordinary waters, 
troubled neither with excessively fine clay turbidity 
nor algae growths, a depth of five feet is best. With 
finer sands four feet may be sufficient. 

Character of Sand .—The sand should be free from 
clay, loam and vegetal matter, and preferably also 
free from particles of limestone and other mineral 
matter that might affect the water injuriously. The 
uniformity coefficient should be as low as possible, 
and the sand grains hard and firm so as not to disin¬ 
tegrate under the action of the water. Sands con¬ 
taining lime and magnesia will render the water 
somewhat harder after filtration. Dirty sands should 
be washed to remove the dirt, before being placed in 
the filters, as such matter would cause clogging and 
reduced efficiency. Particular care should be taken 
to secure sand of uniform character and fineness, be¬ 
cause if several different sizes are used in the same 
bed they will, on account of offering different resist¬ 
ances, cause different rates of filtration in different 
parts of the bed. Also, if the uniformity coefficient 


Plate IX.—Interior View of Ashland, Wis., Covered Filters. Taken when the 

Filtering Sand was being placed in position. 












CONSTRUCTION OF SLOW SAND-FILTERS. 153 

is high there will necessarily be a good deal of sand 
lost during washing, as the velocity necessary to wash 
the larger grains may be great enough to float the 
finer ones away. 

Placing Sand in Filters .—A great deal of care is 
necessary in placing the sand in the filters to secure 
uniform density of the entire bed. It should not be 
deposited in one layer, nor in thin layers, each spread 
out and levelled, but rather in two or three layers, 
the face of each layer being stepped back several feet 
behind the next lower one, and all carried continu¬ 
ously across the bed of the full thickness. After it is 
in place the top should be levelled off to a flat hori¬ 
zontal surface, planks being placed on the sand for 
the men to work on, so that their boots will not com¬ 
pact the surface. 

A view of the Somersworth, N. H., covered slow 
sand-filter, taken when the filtering-sand was being 
placed in position in three layers, is given in Plate X. 

Placing the Gravel .—In placing the gravel around 
the underdrains care must be taken to see that it 
is thoroughly settled before the sand is placed in 
the filter, because subsequent settling may produce 
vertical lamination through the sand, allowing unfil¬ 
tered water to pass down to the underdrains. The 
gravel should be deep enough to bury the lateral un¬ 
derdrains, and should cover the space between them. 
It should not, however, extend clear to the side- 
walls, or edges, of the filters, but should stop 3 or 4 
feet from the walls so as to force the water to flow 
along the bottom of the filter under the sand, as 


154 WATER FILTRATION WORKS . 

was done at Albany by Mr. Allen Hazen. If the 
concrete side-walls are made smooth when first 
built, and are then washed down with a brush 
coat of neat Portland cement, good results 
will be obtained in preventing the too rapid pas¬ 
sage of the water between the sand and wall sur¬ 
face. As stated in chapter III., the walls and piers 
should be battered below the sand line so that the 
sand will settle tightly against them; this provision 
ought to make a tight joint between the sand and 
walls. It is not good practice to plaster the inside 
of the walls of filters below the sand line with a coat 
of cement applied with a trowel, because such coats 
frequently adhere in spots only, leaving spaces be¬ 
hind through which the water can flow if cracks 
should develop in the plastering. Brick walls and 
piers are also to be looked upon with more suspicion 
than if made of concrete, because, as bricks are gen¬ 
erally laid, the mortar cannot be depended upon to 
adhere closely to the bricks in the vertical joints, and, 
therefore, unfiltered water may follow cracks and 
joints to the bottom of the filter. The stopping of 
the gravel layer a few feet from the sides of the fil¬ 
ters is designed to correct this evil. It is also better 
to finish the inside plastering, where it is necessary, 
with a felt float rather than with a trowel, as hard pol¬ 
ished neat-cement surfaces are almost sure to check 
after setting. 

Sand Washing .—In case the sand is dirty and the 
uniformity coefficient too high, it should be screened 
to remove the large- pebbles, and then washed to re- 


o 

»—1 

ft 

> 

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ft 

ft 

r 

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H 

ft 

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ft 

ft 

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r 

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M 

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0 

Z 

ft 

H 

ft 

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ft 

ft 

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ft 

O 

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ft-< 

c: 

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ft 

0 

t-i 

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ft 

ft 

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ft 

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ft 

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ft 


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H 

M 


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ft 



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CONSTRUCTION OF SLOW SAND-FILTERS. I 5 7 

move the dirt. The sand washers in common use by 
contractors, consisting of revolving screens and cylin¬ 
ders with sprays of water playing through the sand, 
are quite effective for removing the clay and dirt. 
They usually have a helix on the interior of the cylin¬ 
der, which works the sand up to the high end, dis¬ 
charging it into cars after it is washed. The dirty 
water and fine particles are washed out at the lower 
end. This form of washer is in use in Berlin. An¬ 
other—and for some reasons a better—washer is the 
form now popularly known as the Hamburg washer, 
from its use in an improved form at the Hamburg 
filters. The washer consists of a series of hoppers 
with ejector nozzles perforating the bottom of each, 
and pipes and troughs arranged so that the sand 
from each hopper is lifted to the next, the fine dirt 
going over the sides of the hoppers with the wash- 
water. This apparatus is shown in sketch in Figs. 
22, 23 and 24, and in the photographic views, Plates 
XIII and XIV, and is the form now used almost ex¬ 
clusively in modern filter plants, because of the con¬ 
venience and thoroughness with which the washing 
of the dirty sand removed after cleaning filter-beds 
can be done. - 

Sand may be washed quite clean with a hose if 
other apparatus is not at hand.. A platform should 
be prepared with walls around all sides, and a mova¬ 
ble-board front. The bottom of the platform may be 
of wood or of brick, and should slope toward the 
open end. The sand is placed in a pile at the high 
end of the platform and the water played on it from 


i 5 8 


WATER FILTRATION WORKS. 



Fig. 22.—Cross-section Through Ejector Sand-washer. 




TO DRAIN WATER 

Fig. 24.—Longitudinal Section Through Ejector Sand- 

washer. 


BOX~TO 
«55'®0 SAND 


SCALE OF TEEf 



















































































































































CONSTRUCTION OF SLOW SAND-FILTERS. I 59 

the hose. The water and dirt overflow the weir in 
front, and the sand remains on the platform. The 
sand is kept thrown back as the washing progresses 
The washing has been carried far enough when the 
wash-water runs clear. The washing is done in this 
way at Antwerp and at some of the London filter 
plants. 

At Edinburgh the sand is washed in boxes hav¬ 
ing perforated false bottoms, the water forced up 
through the perforations carrying the dirt over the 
edges of the boxes. Of course, in all plants experi¬ 
ment is necessary to determine the quantity of water 
necessary to properly wash the sand, and the force 
with which it must be used, so as not to carry off too 
great a proportion of the finer particles. 

The cost of washing sand, and the quantity of 
wash-water required, will be discussed under the 
operation of slow sand-filters. 

Regulating Apparatus .—Generally arrangements 
are made for keeping the surface of the water on the 
filters at a constant height, allowing the water to fall 
in the regulating chamber as the frictional resist¬ 
ances increase with service. This is accomplished 
by placing a valve, operated by a float resting on the 
surface of the water in the filter, on the inlet for raw 
water. In some works, however, the water surface 
in the regulating chamber is kept at a constant level, 
and the depth of the water on the filters is allowed to 
increase, as clogging takes place, while in others the 
water in both the regulating chamber and the filters 
is allowed to fluctuate, arrangements being made to 



i6o 


WATER FILTRATION WORKS. 


prevent too great a depth in the filter by hand- 
regulation of the inlet valve and by an overflow. 
Examples of each kind are to be found in the well- 
known filters of Europe. To the first class belongs 
the apparatus used at Hamburg, to the second the 
older Berlin apparatus, and to the third the auto¬ 
matic devices used at Warsaw and Zurich. Many 
plants have no special apparatus for regulating the 
height of water on the filters, but are worked by 
opening or closing a valve on the feed-pipe, by hand, 
in accordance with the necessities of service. This 
is the case at Zurich, on the earlier Berlin filters, and 
is the general English practice. At Hamburg and 
Leeuwarden, the new filters at Berlin, the Albany 
filters, and at several other places the depth is auto¬ 
matically limited by a float upon the surface of the 
water on the filters. This float opens and closes a 
valve on the inlet pipe. Care should be taken to 
provide some sort of stilling chamber around the 
float, so that it may not be thrown out of line and 
thus jam the valve and cause it to become inopera¬ 
tive. 

In passing through the filters a certain amount of 
head is used up in forcing the water, with the proper 
velocity, through the sand and underdrains. This 
loss of head increases with the length of time the 
fVter has been in service. When the filter will not 
deliver the requisite amount of water, with the maxi¬ 
mum loss of head allowed, the filters must be cleaned. 
In most of the European plants the loss of head is 
limited to from 24 to 36 inches, but in some cases 


CONSTRUCTION OF SLOW SAND-FILTERS. l6l 

9 

these limits are exceeded. There is no reason why 
the loss of head should not be as great as the depth of 
water over the filters, or say from 5 to 6 feet in ordi¬ 
nary cases. When the loss of head is greater than 
the depth of water over the sand, clogging may oc¬ 
cur just below the surface of the sand, on account of 
the accumulation of matter on the surface and the 
liberation of bubbles of air from the water. If the 
regulation of the rate of filtration were done by 
throttling the underdrain before discharging the wa¬ 
ter into the regulating chamber, negative heads could 
be used and greater periods of time between scraping 
would be the result. In other words, the section of 
greatest resistance should be transferred from the 
surface of the sand to the outlet of the underdrains, 
if negative heads are to be used successfully. This 
occurs with some forms of automatic regulating ap¬ 
paratus and hence, with such, negative heads may be 
employed, at least up to the limit of economical con¬ 
struction. 

Regulating apparatuses are of two kinds: those 
operated entirely by hand, and those which are auto¬ 
matic in their operation. Hand-regulators were used 
in England as early as 1839 on the filters built by 
James Simpson for the Chelsea Water Company at 
London. The apparatus consisted merely of a valve 
in the supply-pipe, and one in the discharge-pipe 
from the underdrains. A similar arrangement was 
used at the Stralau works at Berlin, and is in use at 
Edinburgh, Scotland. In the latter place a weir was 
added for gauging the quantity of flow. The outlet 


162 WATER FILTRATION WORKS. 

from the filters at Shanghai is also a simple sluice- 
valve, but an automatic double-seated balanced valve 
on the feed-pipe, operated by a float, keeps the water 
level on the filters at a constant height. It is evident 
that this construction was intended to make the fil¬ 
tration head correspond to the fluctuating draft 
rather than to regulate the flow to a constant rate. 
Similar arrangements are found in most of the early 
filters and in many still in use. 

Another form of regulator much used in the Eng¬ 



lish practice is a telescopic tube, the upper section 
of which can be raised or lowered by a screw. This 
form of regulator is in use at the New River Com¬ 
pany’s filters at London, at the Yokohama water¬ 
works in Japan and at Koenigsberg, in Germany 
(Figs. 25 and 26). In this device a constant dis¬ 
charge, and, therefore, a constant velocity of filtration, 
is insured by so regulating the height of the top of the 
telescopic pipe that a constant depth of water flows 
over its edge. This requires the screwing down of the 
top of the pipe, as the resistances to filtration become 











































CONSTRUCTION OF SLOW SAND-FILTERS. 1 63 

greater with the clogging of the filter. A modified 
form of the apparatus, designed by the Stanwix 
Engineering Company, in 1893, is in use at Ilion, 
N. Y. It consists of a telescopic tube 13 inches in 
diameter, inclosed in a tube 20 inches in diameter, 
the smaller tube being movable and connecting 



Fig. 26.—Regulator in Use at Koenigsberg, Germany. 


through a fixed diaphragm in the 20-inch pipe with 
the pipe leading to the filtered-water reservoir. 

At Antwerp the water from the filter underdrains 
comes out at the tops of telescopic tubes and falls on 
spreaders to promote aeration after having absorbed 
iron in the filter-beds. A similar arrangement has 
also been used quite extensively in Jaf)an by Pro¬ 
fessor Burton. The usual methods of rating the dis¬ 
charge of the telescopic tube are by measurement of 
the amount of water that it discharges, with different 
depths of water over the lip of the pipe, by observing 
the actual quantity by measurement, or by weir 
gauging. 
































































164 WATER FILTRATION WORKS. 

In 1884 Mr. Henry C. Gill designed the regulating 
apparatus for the Lake Tegel filters at Berlin. This 
apparatus is still in use there and also at the new 
Lake Mueggle works. It is shown in Fig. 27. There 



Fig. 27. —Regulator Designed by Henry C. Gill and Used 
at the Berlin Filter Plants. 

are three chambers; the water from the underdrains 
entering freely into the first, then into the second 
through an opening controlled by a valve at the bot¬ 
tom. In the wall of the second chamber a fixed weir 
of known dimensions is placed. After flowing over 
the weir the water falls into the third chamber, which 
connects with the channel leading to the filtered 
water reservoir. A constant depth of water over 
the weir is secured by the operation of the valve in 
the first chamber, which is opened or closed in ac¬ 
cordance with the indications of floats in the different 
chambers and on the water in the filters. By the 
positions of these floats the attendant can determine 



























































CONSTRUCTION OF SLOW SAND-FILTERS. l6$ 

the filtration head, rate of filtration and actual depth 
of water on the filters, and will regulate the valves ac¬ 
cordingly. 

The quantity of water discharged over the weir 
per second of time may be found by the formula 
2 - 

Q = u—~ bh V 2 gh , where Q = cubic feet per second, 

b = width of weir in feet, h = depth of water in feet 
over the weir, measured back of the weir where 
the water is level, g = the acceleration of gravity, 
= 32.2 feet per second, and u — a coefficient to be 
experimentally determined, its approximate value 
being about 0.60, but varying between quite wide 
values with different widths of weir and depths of 
water flowing over it. 

In 1866 Mr. James P. Kirkwood recommended for 
St. Louis an apparatus for regulating the rate of fil¬ 
tration, which consisted of a weir that could be raised 
or lowered until the proper quantity would flow over 
it. This is shown in Fig. 28. The regulating appara¬ 
tus at Hamburg (Fig. 29) is a modification of Kirk¬ 
wood’s, with also a submerged orifice leading from 
the second to the third chambers, through which the 
discharge can be further measured. In the Ham¬ 
burg apparatus a scale is attached to the movable 
weir and a floating index on the surface of the water 
in the chamber shows always the depth of water run¬ 
ning over the weir; the scale also gives the height 
of the water in the measuring chamber relative to 
that in the filters, the water in the filters being kept 
at a constant level by means of a float operating a 



WA TER FIL TR A TION WORKS. 


166 



Fig. 28 . —Regulator Recommended by Jas. P. Kirkwood for 

St. Louis. 


K 

Ul 

b- 

* < 
, * 


Q 



Fig. 29 . —Regulating Apparatus in Use at Hamburg, Ger 
many. F. Andreas Meyer, Engineer. 


FILTER 


TO RESERVOIR 






















































































































































CONSTRUCTION OF SLOW SAND-FILTERS. It)/ 

balanced valve on the supply main. The discharge 
over this weir and also over that of the Kirkwood 
apparatus would be calculated by the formula just 
given for the Berlin apparatus. 

At Albany Mr. Allen Hazen has adopted a method 
of regulation somewhat different from any in use else¬ 
where. (Fig. 30.) The water from the underdrains 



Fig. 30.—Regulating Apparatus Designed by Allen Hazen 

for the Albany Filters. 

enters a chamber, in one wall of which is placed a thin 
plate, with a long, narrow orifice of fixed dimensions 
through its centre. The water flows into the second 
chamber through this orifice; floats resting on the 
water in each chamber show the difference of level be¬ 
tween the water surface each side of the plate, and 
from this difference of level the discharge can be 
computed. Indexes and scales connected with the 
floats show the filtration head and the rate of filtra¬ 
tion. When the water in the second chamber falls be¬ 
low the centre of the orifice, the float in that chamber 
is prevented, by an ingenious arrangement, from 














































i68 


WATER FILTRATION WO RE'S. 


sinking lower than that point, and the discharge 
through the orifice is then a free discharge into the 
air. The size of the opening is so proportioned that 
a certain maximum rate of filtration may not be ex¬ 
ceeded in service. The regulation of the rate of flow 
is effected by valves worked by hand. So long as a 
constant difference of level is maintained between the 
water surfaces either side of the orifice, a constant 
discharge will ensue. With a little care the rate can 
be regulated very closely. 

Automatic regulators may be classed in two 
groups: those operated by the action of floats on the 
surface of the filtered water and those in which, with 
varying rates of draft, the velocity, or energy of the 
water, as it is drawn from the filters, is made to effect 
its own regulation by opening or closing a balanced 
valve. 

Of the automatic regulators operated by floats, 
those at Zurich (Fig. 31) and Warsaw (Fig. 32) 
are the most prominent of the European types. In 
each there is a telescopic joint of pipe, having ver¬ 
tical slits around the periphery at the top, suspended 
from a float. The float swims on the surface of the 
filtered water in the regulating chamber, and the 
filtered water escapes to the reservoir through this 
telescopic pipe. If the top of the pipe is kept at a 
constant depth below the surface of the filtered water 
a constant flow will be established. The depth of im¬ 
mersion of the pipe in the Zurich apparatus is gov¬ 
erned by a screw which alters the relative height 
of the float and pipe. The float carrying the pipe is 


CONSTRUCTION OF SLOW SAND-FILTERS. 169 

free to move vertically, the screw-stem being square 
above the float and sliding through the hub of the 



Fig. 31. —Regulator in Use in Zurich, Switzerland 

M. Peter, Engineer. 



Fig. 32. —Regulator Designed by Mr. Wm, H. Lindley for 
the Filters at Warsaw, Poland. 

gear wheels above. In the Warsaw apparatus, de¬ 
signed by Mr. William H. Lindley, the relative po- 































































































170 WATER FILTRATION WO RETS. 

sitions of float and pipe are fixed and the rate of dis¬ 
charge is regulated by a collar, the moving of which 
opens or closes an orifice at the top. To Mr. Lind- 
ley is due the credit of first advocating the separate 
and automatic regulation of slow sand-filters. 

A modification of Mr. Lindley’s regulator (Fig. 
33) was proposed for the regulation of the filters for 



Fig. 33.—Type of Regulator Suggested by the Mayor’s 
Expert Water Commission for Philadelphia, Pa. 

Philadelphia. The difficulty with these automatic 
devices is that sometimes the floats are not given 
sufficient margin of buoyancy to overcome instantly 
the friction of the packing around the telescopic pipe, 
as the water level changes in the regulating chamber, 
and this may affect the depth of immersion of the 
tube and consequently the rate of discharge. For 























































































CONSTRUCTION OF SLOW SAND-FILTERS . 171 

this reason deep, narrow slots around the periphery 
of the tube are better than wide shallow ones, the 
discharge through the former being affected in a 
lesser degree for a given change of depth of immer¬ 
sion than through the latter. With proper details 
of design and construction this trouble can be recti¬ 
fied. 

The regulator shown in Fig. 34 was designed by 



Fig. 34.—Regulating Apparatus Designed by the Author 
for the Tome Institute Filters. 

the author for the Tome Institute filters. The water 
from the filters discharges into a well through which 
the pipe leading to the filtered-water reservoir rises 
to above the level of the water on the filters. A rect¬ 
angular orifice is cut through one side of the pipe on 
line with its central horizontal axis. The orifice is 







































172 


WATER FILTRATION WORKS. 


formed in a thin plate with beveled edges, and one 
side is movable vertically, like a slide. This slide is 
attached to a rod connecting with the end of a lever 
operated by a ball-float and pivoted to the pipe. As 
the water-level in the well rises the slide will close the 
orifice proportionately. The size of the orifice is 
such that if the water-level in the filtered-water reser¬ 
voir were below the orifice, the rate of discharge 
would be constant whether the water in the well stood 
6.5 feet or .5 foot above the orifice, and this rate 
would be 50 per cent, greater than the rate at which 
the filters are to operate normally. When the draft 
on the filters is normal the orifice is submerged. If 
the draft is below normal the filters are automatically 
and slowly shut off. 

In all the foregoing forms of automatic regulator 

the discharge from the beds is free, and the differ¬ 
ence in level between the water on the filters and in 

the chambers adjusts itself automatically to the in¬ 
creasing resistances. 

The apparatus used at Worms (Fig. 35), operated 
by a float on the surface of the unfiltered water, re¬ 
quires constant adjustment as the resistances in¬ 
crease, and does not, it would seem, offer the advan¬ 
tages given by the more simple forms used at War¬ 
saw and Zurich. 

The automatic regulator, designed by Professor 
W. K. Burton, and shown in Fig. 36, utilizes the ve¬ 
locity of the water, as it is discharged from the filter, 
to effect its own regulation. It is in use in the filters 
at Tokio and Osaka, Japan, and consists of a bal- 


CONSTRUCTION OF SLOW SAND-FILTERS. 173 





Fig. 35.—Regulator in Use at Worms, Germany. 



Fig. 36.—Regulator Designed by Prof. W. K. Burton and 
in Use at Tokio and Osaka, Japan. 










































































































































174 WATER FILTRATION WORK’S. 

anced valve opened or closed by differences in pres¬ 
sure on the opposite sides of a piston attached to the 
valve-stem. This difference of pressure is induced 
by placing a diaphragm, with an orifice in its centre, 
in the outlet of the underdrain pipe. In passing 
through this orifice the flow of the water is retarded; 
this produces pressure on the lower side of the pis¬ 
ton, as a consequence of which the valve is closed au¬ 
tomatically. 

There is still room for the exercise of inventive ge¬ 
nius in the improvement of the regulating apparatus 
for slow sand-filters. Some reliable arrangement 
which, while preventing a certain maximum rate 
being exceeded, would automatically permit the use 
of any rate below the maximum, at the same time 
giving a continuous record of the actual rate, would 
be very useful. Such an apparatus would allow the 
filters to adjust themselves to some extent to the 
rate of draft. As has already been explained, this 
practice has been found to be safe, between certain 
limits, and gives to the plant a flexibility in opera¬ 
tion that at times may be very desirable. 

Cost of Slow Sand-filters .—The cost of construc- 
ing slow sand-filter plants depends entirely upon local 
conditions. It is convenient to refer the cost to a 
unit of area rather than to a unit of quantity of water 
filtered, because some waters may be filtered more 
rapidly than others, and hence the cost per million 
gallons filtered would not be a satisfactory unit for 
comparison. The cost per acre of filter surface, how¬ 
ever, is a very convenient and expressive unit, as 


CONSTRUCTION OF SLOW SAND-FILTERS. 175 

from it an idea may be mentally and rapidly formed 
of the cost of a proposed plant. Small filter-beds 
naturally cost more per acre than large ones, be¬ 
cause, while the cost of floors, roofs and piers will be 
about the same per acre of area, the volume of ma¬ 
sonry in the side-walls of small filters will be much 
greater in proportion to the area than in the large 
ones. 

Among the features that influence the cost of filter 
plants are the rate at which they are to be operated, 
the arrangement of the beds, the topography and ge¬ 
ological structure of the region, the local prices of 
materials and labor, the legal length of a day, the ex¬ 
penses of administration, the season of the year in 
which the work is undertaken, the rate at which the 
work will have to be pushed and the difficulties in the 
transportation of materials and the securing of labor. 

It is generally found that the filters should be so 
placed that the water level, when the filters are filled, 
will be about at the level of the natural surface of the 
ground. It also seems to make little difference in the 
cost of excavation whether the filters are built on 
level ground or on sloping ground, with the beds 
stepped down in terraces, even when there is con¬ 
siderable difference in elevation between different 
parts of the area. For instance, in the data given 
in Table XII, the differences in elevation of the nat¬ 
ural surface of the ground in different parts of plants 
Nos. i and 2 was fifteen feet; in plants Nos. 3 and 4, 
ten feet; in plant No. 5, thirty feet, and in plants Nos. 
6 and 7, five feet. In plant No. 8 the excavation was 


176 


WATER FILTRATION WORKS . 


nearly all slate rock. In plants Nos. 9 and 10 there 
was also a large amount of rock excavation. 

Data, concerning the cost of filter plants, derived 
from works in operation, must be interpreted with a 
thorough understanding of what these costs include, 
and a knowledge of the local conditions. Some 
works, very simple in design, requiring no pumping 
machinery, no difficult foundations and no excessive 
haul on materials, can be built cheaply, while others, 
where the conditions are not so favorable, may cost 
much more. In the estimates of cost of the filter 
plants for the improvement of the Philadelphia 
water-supply, the transporting of the materials to the 
filter siteswas an item of considerable magnitude. Its 
effect, exclusive of the hauling of the piping, was to 
increase the cost of the remote plants at the rate of 
about $4,500 per acre above the cost of the plants 
more favorably located; the beds were covered and 
had an area of f acre each. It is necessary therefore 
when the plant is to be built at a point where consid¬ 
erable difficulties attend the delivery of materials, to 
add to their cost the expense of transporting them to 
the site of the works. 

In Table XII are classified the unit costs per acre 
of some of the component parts of several large filter 
plants in the United States for which estimates of 
cost have recently been made. All the filters were 
to have been covered and to have an area of about 
5 acre each. The estimates do not include the cost of 
the piping to and from the filters, the cost of 
pumping plants, of sedimentation basins or filtered- 


CONSTRUCTION OF SLOW SAND-FILTERS . 177 

water reservoirs, but do include the making of roads, 
sodding of embankments, seeding of lawns, and all 
work connected with the filters, including the un¬ 
derdrains, filtering materials, regulating apparatus, 
etc. 

TABLE XII. 


c 

a 

E 

Number 
of Beds. 

Excava¬ 

tion, 

including 

Sodding, 

Seeding, 

etc. 

Sand- 
washers, 
including 
Piping for 
Wash- 
water. 

Covered 

Filters 

Comolete, 

including 

Filtering 

Materials, 

etc. 

Electric- 

lighting 

Plant. 

T ram ways 
for Sand- 
Hauling, 
including 
Cars. 

Resi¬ 
dences, 
Shelters, 
Offices, 
Fences, 
Store¬ 
rooms, etc. 

1 

13 

$3,200 

$328 

$ 50,313 

$640 

$ 536 

$3600 

2 

26 

3,200 

276 

44,348 

772 

572 

2308 

3 

8 

3,208 

368 

50,6l6 


468 

5136 

4 

18 

2,852 

336 

50,412 


444 

2068 

5 

27 

3.276 

276 

49 , 8^8 

740 

588 

1904 

6 

24 

3,076 

312 

50,228 


540 

2136 

7 

i 3 3 

3,040 

336 

49,808 


528 

1448 

8 

136 

24,716 

412 

50,000 

i 5 7 o 

6.6 

1508 

9 

133 

8,000 

280 

50,000 

1200 

452 

1416 

10 

70 

16,048 

290 

46,668 

1240 

536 

1500 


The Albany covered filters cost about $38,000 per 
acre, including the filtering materials, but excluding 
the excavation, sand-washing machinery, buildings, 
pumps, settling basins, and piping to and from the 
filters, and about $45,600 per acre, including all the 
above items, except the pumps and sedimentation 
reservoirs. Small plants cost very much more in 
proportion than large ones. For instance, for a plant 
consisting of three open filters, with a total area of 
0.19 acre, the actual costs per acre were as follows: 


Excavation, grading, etc. $8,200 

Sand-washing machinery. 8,400 

Filter-beds, including sand, etc. 100,000 

Tramways and equipment. 816 




























178 IV.A TER FILTRATION IVOR NS. 

For another plant consisting of two very small cov¬ 
ered filters with a total area of 0.013 acre, the costs 
per acre were as follows: 

Excavation, grading, etc. $17,000 

Covered filters, including sand, etc.. .. 115,400 

The cost of the Nyack filters with a total area of 
0.38 acre was, for excavation, including foundations, 
sheet piling, etc., $30,500 per acre, and for the open 
filters complete $46,700 per acre. The covered slow 
sand-filters at Ashland, Wis., with an area of half an 
acre, cost at the rate of a little under $70,000 per 
acre. 

Statements of cost per acre must therefore be in¬ 
terpreted understanding^. The necessary piping, 
the drains, auxiliary pumping machinery for lifting 
the water to the filters from the settling basins, or 
into the settling basins from the source of supply, 
the land, buildings and other necessary adjuncts may 
amount to nearly as much as the cost of the filters. 
These conditions are so varying that statements of 
their cost in individual cases would be of little value 
here. The cost of the bacteriological and chemical 
laboratories cannot well be stated in a price per acre, 
because one laboratory generally serves an entire 
municipal plant, and requires about the same equip¬ 
ment for a small plant as for a large one. The cost 
of such a laboratory, properly equipped, is about 
$30,000, but may be more or less than this by a con¬ 
siderable amount, according to circumstances. 

The cost of roofing the Albany filters, including 



OPERATION OF SLOW SAND-FILTERS. 179 

the piers, was about $0,315 per square foot, or a little 
under $14,000 per acre. In the estimates given in 
the preceding tabulation the cost of the roofing was, 
in most cases, very close to this figure. 

OPERATION. 

For convenience in operating the plant it will be 
advantageous to place the filtered-water reservoir 
at such a height that the filtered water may be con¬ 
ducted to it by gravity. The highest water level in 
the reservoir should be such that it will not cause 
back water on the filters and thus limit the filtration 
head in the different beds when the plant is operat¬ 
ing at its maximum capacity. Such an arrangement 
will permit the filters to operate independently when 
the draft is normal, while at the same time it will 
cause the water level in the reservoir and regulating 
chambers to rise when the draft falls below normal, 
slowly and automatically reducing the filtration head 
on the filters and affecting those first which have 
been longest in service. Upon the draft again being 
increased the water level in the reservoir will fall and 
the rate of filtration in the different beds will grad¬ 
ually be increased to the rates at which they were last 
operating. This principle is applicable to both the 
automatic regulators and the submerged-orifice ap¬ 
paratus designed for the Albany filters by Mr. Allen 
Hazen. The effect of the gradual changing of the 
rate of filtration between reasonable limits has al¬ 
ready been shown to have no bad effects on the qual- 


l8o IV.A TER FILTRATION IVOR NS. 

ity of the effluent, while the adoption of such a plan 
offers many advantages. 

Scraping Slozv Sand-filter Beds .—After a filter-bed 
has been in operation for a considerable time it be¬ 
comes so clogged at the surface that the water can¬ 
not pass through it at the prescribed rate. When 
this time comes it is necessary to put out of service 
and clean the bed. The first operation will be to drain 
off the raw water standing above the sand, and lower 
its level below the surface of the filter so that the 
workmen may enter after the sand is hard enough to 
bear their weight. Cleaning is now done by hand, 
although undoubtedly improvements in methods 
will be brought out as filter plants multiply. The 
workmen are furnished with broad flat shovels or 
scrapers with which they skim off the dirty top layer 
of the sand to sufficient depth to remove the clog¬ 
ging—from f inch to a little over an inch, generally, 
averaging perhaps somewhat less than f inch. The 
method is illustrated in Plate XI. This material is 
heaped up in piles on the surface of the filter and then 
removed in wheelbarrows on plank runways, or in 
cars running on movable tracks. In some cases the 
dirty sand is lifted out of the manholes of covered 
filters by derricks. Wheelbarrows are generally used 
in small plants, and in large ones wheelbarrows to 
get the sand to the tramway, and cars from there to 
the sand-washers. The sand, as it is removed, is taken 
to the court and deposited in piles near the sand- 
washers. The washing is done only in warm weather, 
the winter’s accumulations being allowed to stand 


Plate XI.—Method of Scraping Slow Sand Filters. 











OPERATION OF SLOW SAND-FILTERS. 183 

over till spring. Storage-room for this material must 
therefore be provided, as washing can not be prop¬ 
erly done in freezing weather. 

The cost of the labor of scraping filters varies con¬ 
siderably in different plants and in different coun¬ 
tries. 

Mr. George I. Bailey gives the following data* for 


the Albany plant: 

Average depth of sand removed at each scraping. | in. 

Hours of labor to scrape 1 acre.67 

Wheeling out scraped sand; average haul going and coming, 

600 feet; speed per man per hour.1.18 miles 

Quantity of sand wheeled out per hour’s work.0.38 cu. yd. 

Quantity of sand washed per hour’s work.0.41 cu. yd. 

Quantity of water used for washing sand.12-14 volumes 

Quantity of sand replaced per hour's work.0.52 cu. yd. 


Quantity of water filtered between scrapings, 66,600,000 gallons 
per acre of filter surface. 

•The refilling was done mostly by extra labor. 

Cost of Scraping .—The time required for scraping 
an acre of filter surface ranges from 65 hours to 
about 300 hours in the different plants from which 
the author has been able to obtain data; a fair and 
ordinarily attainable result with covered filters 
would be about 175 hours per acre. The annual 
deep scraping requires much more time than this and 
may be estimated by the cubic yard when the quan¬ 
tity to be removed is known. Ordinarily, at such 
times, the sand will have to be taken out for a depth 
of from 4 to 8 inches, but in some cases it may be 
necessary to remove it all down to the surface of the 


* Trans. Am. Soc. C. E., vol. xliii. p. 296. 











184 WATER FILTRATION WO RATS. 

gravel. At Lawrence, Mass., in 1898, the filters be¬ 
came partially clogged, so that their capacity was 
considerably reduced. An investigation by the State 
Board of Health revealed in the gravel a growth of 
crenothrix, which had caused a deposit of iron-rust 
to such an extent around and between the stones 
that the water could not pass freely into the under¬ 
drains. The growth of crenothrix was found to be 
due to the pumping of the water away from the fil¬ 
ters too rapidly, thus unduly lowering its level and 
permitting air to enter the underdrains. The trouble 
was rectified by excavating a large part of the area 
and renewing the underdrainage system. 

After the annual deep scraping it is customary to 
loosen up the remaining sand for a depth of several 
inches and allow the filter to stand for some time, 
several days in some instances, before refilling with 
washed sand. The surface, after scraping, is raked 
over to make it level and smooth and to remove the 
prints of the workmen’s boots. In some places, par¬ 
ticularly in England, it is customary, once a year, to 
trench the sand down to the gravel, filling the 
trenches with washed sand, and afterward covering this 
with the sand taken from the trenches. Experiments 
have also been made with the “seeding” of the beds 
after scraping by spreading a thin layer of partially 
clogged sand over the filters to start the biological 
action more quickly, but so far as I have been able 
to learn the process has not proven of any advantage. 

The quantity of sand removed at a scraping, as¬ 
suming the layer taken off to be f inch deep, would 


OPERATION OF SLOW S. AND-FILTERS. I 85 

be about 50^ cubic yards per acre. If it were nec¬ 
essary to scrape 13 times during the year, includ¬ 
ing the annual deep scraping, and if the latter were 
4 inches deep, the quantity of sand removed, per 
acre, would be about 1,150 cubic yards, equivalent 
to an average depth of 8^ inches. At Lawrence 
the quantity has been slightly less than this. 

Frequency of Scraping .—The frequency with which 
scraping will be required depends principally on the 
character of the water, being necessary more fre¬ 
quently at some seasons of the year than at others. 
The following table, compiled from the reports of 
the Lawrence Water Board for 1897 and 1898, show 
the number of times each of the filter-beds was 
scraped during these two years. 

TABLE XIII. 







































1 86 WATER FILTRATION WORKS. 

The average number of scrapings at Lawrence has 
been about 14 per year. 

In Zurich, notwithstanding the clearness of the 
lake water, the filters require scraping quite fre¬ 
quently at times, on account of the presence of cer¬ 
tain organisms in the water in the summer season 
which clog the surface of the sand very rapidly. The 
following tabulation exhibits the data regarding the 
scraping of the Zurich filters for several years. 


TABLE XIV. 


Year. 

Days between Scrapings. 

1894. 

7 Filters. 

1895. 

7 Filters. 

1896. 

10 Filters. 

1897. 

10 Filters. 

Minimum. 

9 

5 

5 

6 

Maximum. 

47 

28 

42 

64 

Average. 

21 

13 * 

17 

17 

Average number of scrap- 
ings per year of each bed. 


23 

18 

21 


At the Lake Tegel works in Berlin the minimum 
period of time between scrapings, that is, when algae 
growths are most flourishing, is about 10 days; the 
maximum period is about 80 days, occurring in the 
winter time, and the average period 30 days. At 
Altona the minimum period is 10 and the maximum 
50 days. 

Where scraping would be required oftener, on the 
average, than twice a month, it may generally be as¬ 
sumed that some preliminary treatment before 
filtration would be advisable. This may be sedimen¬ 
tation, with or without coagulation, or some other 






















OPERATION OF SLOW SAND-FILTERS. 1 87 

measure for the removal of the suspended matter or 
growths of algae in the water. 

In existing plants the quantity of water filtered 
between scrapings, where the water has had proper 
treatment before being admitted to the filters, 
ranges from about 40 to 100 million gallons per acre. 
At Stralau, Berlin, in 1893, the quantity delivered 
by the open filters between scrapings during the pe¬ 
riod when algae growths were most flourishing was 
on one occasion reduced to only 14 million gallons 
per acre. 

Effect of Covers on Frequency of Scraping .—In 
Zurich it was found that the open filters required 
scraping more often than those which were covered. 
In 1887 the average period between cleanings of the 
covered filters was 77 days, while the uncovered 
filters required cleaning on the average every 48 
days. In 1892 and 1893 both kinds of filters were 
cleaned more frequently than in 1887, yet the open 
filters required the treatment at shorter intervals 
than the covered ones, as is shown by the following 
tables taken from the Stadtrat Report of 1893: 

TABLE XV. 


NUMBER OF DAYS BETWEEN CLEANINGS. 



Covered Filters. 

Open Filters. 


1892. 

1893. 

1892. 

1893.* 

Minimum. 

19 

12 

II 

13 

Maximum. 

69 

73 

50 

39 

Average. 

36 

27 

23 

20 


* 1893 to the middle of September. 
























188 


WATER FILTRATION WO RETS. 


TABLE XVI. 

GALLONS OF WATER FILTERED BETWEEN CLEANINGS. 



Covered Filters. 

Open Filters. 


1892. 

1893. 

1892. 

1893. 

Minimum... 
Maximum .. 

26,420,000 

76,618,000 

9,168,000 

116,658,000 

19,419,000 

47,952,000 

13,606,000 

51 , 572,000 

Average.. 

44,914,000 

31,255,000 

29,855,000 

21,532,000 


A thick layer of green algae would frequently grow 
upon each of the uncovered filters. This growth not 
only rapidly clogged the filters, but also gave much 
trouble in other directions. The rising of bubbles 
of gas through the water, tearing loose and carrying 
with them patches of the algae growths, would disturb 
the surface of the filters and allow raw water to 
pass through the bald patches too rapidly. The cov¬ 
ered filters were not troubled in this way, because the 
algae could not grow in the dark. 

In regard to the growth of algae on filter surfaces, 
Mr. Charles E. Fowler, Superintendent and Engi¬ 
neer of Public Works, Poughkeepsie, N. Y., says: * 
“ The algae growths on the sand in summer are quite 
as troublesome and almost as expensive as ice and 
frost in winter. Like ice, they can develop on an 
unlimited area in the same time as on a small unit, 
and will stop a filter and put it out of service just 
when it should otherwise be doing its best work.” 

The studies of Dr. Otto Strohmeyer of the growths 
of microscopic organisms in the sand of the Ham¬ 
burg filters, and of Dr. Ad. Kemna, of Antwerp, 


* Trans. Am. Soc. C. E., vol. xliii. p. 311. 























OPERATION OF SLOW SAND-FILTERS. 1 89 

along similar lines, have brought out, among other 
things, the very interesting facts that when the vege¬ 
tation over the sand surface is in a living condition 
it is a decided aid to the efficiency of the process of 
filtration, if it does not result in a disturbance of the 
sand surface, and that some of the algae exercise a 
sterilizing influence on the water in which they are 
growing; also that the flora change with the sea¬ 
sons, and that the decomposition of certain of the 
organisms, with seasonal changes, notably Ana- 
boena, causes a bad taste in the water. Mr. George 
C. Whipple, Director of the Mount Prospect Labora¬ 
tory of the Brooklyn Water-works, has also noticed 
that when the growth of some of these organisms, 
particularly Asterionella and Synedra, was luxuriant 
in the Brooklyn reservoirs the number of water bac¬ 
teria was unusually low. It may thus be that some of 
these growths exercise a sterilizing influence on the 
water, and, therefore, assist in its purification, but it 
is always at increased cost of operation of the filters 
on account of the more rapid surface clogging. 

At Antwerp the algae growths are watched care¬ 
fully, and the filters are operated slowly during the 
season when such growths are most vigorous, be¬ 
cause the evolution of gases breaks loose -large 
masses of the organisms, which, floating to the sur¬ 
face, carry with them parts of the surface film, and 
leave bare portions of the unclogged sand, through 
which the water may pass, imperfectly filtered. These 
facts should in each case be considered in deciding 
whether or not covers for filters are advisable. 


190 WATER FILTRATION WORKS. 

I 

Transportation of Sand to Washers .—The cost of 
transporting the sand from the filters to the sand- 
washers and back will depend upon the distance the 
materials have to be moved and upon the means 
employed for their transportation. Where wheel¬ 
barrows are used the cost may range from 20 cents 
to 40 cents per cubic yard, each way; if cars are used 
the cost may be considerably less than this, and a 
still further reduction may be possible if water-car¬ 
riage is feasible. 

In Plate XII is given a view of the Albany, N. Y., 
filters, showing the wheeling-gang removing the 
scraped sand from the filters to the sand-court. This 
is done by “ stint work,” for which time and one half 
is paid. The best record of the gang is as follows: 

7.5 barrows per cubic yard. 

10.5 barrow-loads per hour’s work. 

0.087 miles per barrow-load. 

The sand-washers, as originally built, are shown in 
Plate XIII. The dirty sand was wheeled to the wash¬ 
ers from the heap in barrows. In Plate XIV is shown 
an improvement, recently introduced, by which the 
transportation is done in flowing water instead of 
wheelbarrows. A portable ejector hopper has been 
added to the washers, so that the dirty sand may be 
conveyed from the heap to the washers without the 
use of wheelbarrows. 

Cost of Sand Washing .—After the sand is taken to 
the ejector washers one man can feed it in as fast 
as two can take it away after it is washed; the extra 


Pla i e XII. Albany, N. Y., Filtration Plant. Wheeling out Sand removed 

from Filters after scraping. 


















Plate XIII. Alban\ ^iliraiion Plant; Sand Washers as originally built. The 
dirty Sand was wheeled in Wheelbarrows to the Washers 













Plate XIV.—Albany Filtration Plant. Improvement in Sandwashing Machinery. 
The Sand is conveyed to the Washer through a Pipe by a movable Ejector 
Hopper and a Stream of Water. 



















OPERATION OF SLOW SAND-FILTERS. 197 

labor amounts to about the time of another man, or, 
say four men to wash from 16 to 30 cubic yards of 
sand per day, or from 0.40 to 0.75 cubic yard per 
hour's work. Washing the sand with water under 
pressure, in ejector hoppers, takes from 12 to 15 vol¬ 
umes of water to one of sand washed, or, say 325 to 
400 cubic feet of water to the cubic yard of sand. This 
amounts to about one half of 1 per cent, of the water 
filtered, counting the scrapings about three quarters 
of an inch deep and the quantity filtered between 
scrapings about 80,000,000 gallons per acre. An 
allowance of 1 per cent, of the water filtered for wash¬ 
ing sand and wasting will generally be ample. 

The Trommel washer, or revolving drum, used at 
Berlin, is 11 feet long, about 4 feet in diameter, and 
when turning at the rate of 7 revolutions per minute 
will wash 4 cubic yards per hour; 4 to 5 men are 
required for operating it, and about 350 to 390 cubic 
feet of water are required for properly washing a 
cubic yard of sand. The cost of washing the sand is 
given as 315 cents per cubic yard, including the de¬ 
livery to and removal from the washer. 

The washing of the sand is generally done with 
filtered water from the mains, but this is not abso¬ 
lutely necessary, as ordinarily the raw water, unless 
exceedingly polluted, will give satisfactory results. 

If the sand is very fine, or can be had very cheaply, 
it may not, under some circumstances, pay to wash 
the sand removed during the periodical scrapings. 
In such cases new sand is used in refilling. 


lgS WATER FILTRATION WORKS. 

Lost Sand .—In washing the sand a certain amount, 
depending upon the uniformity coefficient, is lost by 
being carried away in the wash-water. Reliable data 
bearing on this subject are difficult to obtain, but 
such statements as have come under the author’s ob¬ 
servation lead to the belief that from about 3 to 10 
per cent, of the sand washed is lost in this way. These 
figures may be high for plants using coarse, uniform 
sands, but they are certainly not high for those using 
very fine sands. The amount lost may be controlled, 
to a certain extent, by carefully regulating the quan¬ 
tity of sand fed to the hoppers, the quantity of water 
used in washing it, and the pressure of the water. 
The effect of repeated washings is to slightly increase 
the effective size of the sand and reduce its uniformity 
coefficient. 

Ice on Open Filters .—Where ice has formed over the 
water on open filters the general custom is to remove 
it before scraping, but at Hamburg the cleaning is 
done with a Mager scraper, a bag having a sharp lip 
across the edge of the open end. This bag is sus¬ 
pended from a float and is dragged back and forth 
across the filter, by means of ropes, allowing the 
water and ice to remain on the filters. The process 
is reported to be satisfactory. The removal of the 
ice from such large beds as those at Hamburg would 
be attended with much inconvenience, not only in the 
handling of the ice, but in finding a place to store it 
on the banks. 

The scraping of open filters in freezing weather is 
generally very unsatisfactory from all points of view. 


OPERATION OF SLOW SAND-FILTERS. 199 

The freezing of the surface of the sand makes it im¬ 
possible to remove a layer of the same thickness over 
the whole area, and also may cause a very considera¬ 
ble reduction in the efficiency of filtration by the frost 
extending down into the bed several inches and form¬ 
ing cracks through which the water may start to fil¬ 
ter so rapidly as to wash the clogging matter out and 
leave spots of less age biologically than the main 
body of the filter. The difficulty from freezing, how¬ 
ever, does not follow until the temperature is several 
degrees below the freezing point. 

Covers for filters may also conduce to economy in 
operation in point of the amount of sand removed in 
cleaning during the summer time as well as during 
the winter. In the open type, on account of the bak¬ 
ing of the surface of the filter in the summer under 
the action of the hot sun, it is often impossible to re¬ 
move as thin a layer of sand in scraping as could be 
easily taken off if the baking were prevented. 

Refilling after Scraping .—After the filters have 
been scraped they are refilled with filtered water 
through the underdrains, the water passing upward 
through the filtering material until it stands a few 
inches above the sand. The filter is then allowed to 
stand for a longer or shorter time before again being 
placed in operation. This method is much more sat¬ 
isfactory than the older one of filling from above with 
raw water. In the latter method sub-surface clog¬ 
ging and channels, through which the water may 
pass freely to the underdrains, are apt to be produced 
by the entrainment of air bubbles and their rising 


200 


WA TER FILTRATION WORKS. 


through the filters. It is also almost impossible to 
pass the water over the surface of a filter without 
washing furrows in the sand. This necessitates the 
wasting of a considerable amount of the water first 
passing through. 

Double Filtration .—For the purpose of removing 
turbidity and to prevent the clogging of the filters by 
algae growths, double filtration has been practised at 
Altona, Bremen, Schiedam and Zurich. At Altona 
it was not found to be of much advantage, but at 
Bremen it has proven satisfactory. As generally 
carried out, the method of operation is to pass the 
filtrate from a new filter, or one which has recently 
been scraped, through another filter that has been in 
service for some time. With some waters this pro¬ 
cess will not prove advantageous, because of the re¬ 
moval from the water, by the first filter, of the con¬ 
stituents necessary for the production of the surface 
film. 


CHAPTER V. 


THE PURIFICATION OF WATER BY RAPID 
SAND-FILTRATION. 

THEORY OF RAPID SAND-FILTRATION. 

The Coagulant and its Effect on the Efficiency of Fil¬ 
tration .—The discussion which has preceded has had 
reference only to what takes place naturally in beds 
of sand when water is passed through them at com¬ 
paratively slow rates. An attempt to pass water very 
rapidly through such beds would, in a short time, re¬ 
sult in filling up the pores of the bed and producing 
an effluent no better, and possibly even worse, than 
the raw water. If, however, a coagulant be intro¬ 
duced into the water, before it is passed through the 
filters, a considerable degree of purification can be 
accomplished. Sulphate of alumina has, so far, been 
found to be the most suitable coagulant for the pur¬ 
pose. This compound, when mixed with water con¬ 
taining a small amount of lime or magnesia, breaks 
up, forming sulphuric acid and aluminum hydrate. 
The sulphuric acid unites with the alkaline constitu¬ 
ents of the water, while the hydrate of alumina acts as 
a coagulant, gathering together in flocculent masses 
the particles of suspended matter in the water. The 

s 201 


202 


WATER FILTRATION WORT'S. 


hydrate of alumina is a sticky, gelatinous substance, 
which adheres to the grains of sand as the water 
passes through the filter, and catches and holds in 
its mass the bacteria, as well as the particles of clay 
and other suspended matter in the applied water. 
Upon this coagulating material depends the efficiency 
of the well-known mechanical or rapid sand-filters. 

As before stated, the aluminum hydrate forms a 
film of gelatinous or jelly-like material over the top 
of the sand, as well as around each grain, through 
which the water must pass and come into intimate 
contact in passing down through the filter. The sus¬ 
pended matter, including the bacteria, will be re¬ 
tained in the body of the filter. After a certain period 
of service the filter will become clogged. The clean¬ 
ing is done by agitating the bed of sand, and at the 
same time forcing pure water upward through it. 
The wash-water, containing the impurities that have 
been retained in the bed, is wasted, or turned into 
settling basins. 

For a number of years experimenters have been 
trying to produce a cheap, effective coagulating ma¬ 
terial. Efforts have also been made to cheapen the 
present processes for the manufacture of sulphate of 
alumina, but there seems to be no immediate pros¬ 
pect of greatly decreasing its cost by radical changes 
in methods of manufacture; increased demand, how¬ 
ever, would undoubtedly lessen the price in the 
course of time. 

For the removal of turbidity only, the hydrate of 
iron is an excellent coagulant, but as it is more ex- 


THEORY OF RAPID SAND-FILTRATION. 203 

pensive than alum, and less efficacious in removing 
color, it is not used extensively in connection with 
rapid sand-filters in the United States. 

The only objection that has been seriously urged 
against the use of alum has come from physicians 
who have believed that the passage of the alum into 
the distribution pipes in the city, at times when the 
alkalinity of the water was too low to decompose the 
entire charge of chemicals being used, might act in¬ 
juriously on the public health. The only answers to 
this charge are: that there should be no such acci¬ 
dental overdose in a properly managed plant, and 
that there are now hundreds of these filters in use for 
small municipal supplies where the charge of the 
chemicals is not carefully watched, and yet there is 
not recorded a single instance where it is proven that 
the health-tone of the community has been lowered 
by the use of water filtered with the aid of alum. 

Quantity of Coagulant Required .—The efficiency of 
the process of rapid sand-filtration depends upon the 
quantity of coagulant used, the time of its application 
to the water, the composition of the water, the 
amount of subsidence allowed, the thickness of the 
sand layer in the filter, the size of the sand grains, the 
rate at which the filter is operated, the loss of head 
allowed at the filters, the manner of washing the fil¬ 
ters and of operating them, and the care and over¬ 
sight exercised at all times over all stages of the 
process. 

The effect of using too small a quantity of coagu¬ 
lant will be a low efficiency in the removal of bac- 


204 WATER FILTRATION WO RES. 

teria, turbidity and color. The quantity of coagulant 
used should always be less than corresponds to the 
alkalinity of the water; in other words, if there is not 
enough carbonate of lime or magnesia in the water 
to neutralize the sulphuric acid set free by the chem¬ 
ical reactions, the acidulated water will attack the iron 
and lead pipes, in the distribution system, and may 
cause a great deal of trouble. If there is not enough 
lime in the water, at most seasons of the year, to per¬ 
mit sufficient coagulant to be used, this process will 
generally not be suited for its purification, as the ex¬ 
pense of continuously adding lime or soda-ash, to¬ 
gether with the cost of the sulphate of alumina treat¬ 
ment, would probably be higher than the cost of other 
processes of purification. 

Where the water is ordinarily of proper composi¬ 
tion, but may be deficient in alkalinity during heavy 
floods, lime or soda may then, in some cases, be sup¬ 
plied before adding the alum solution. The waters 
of rivers and streams generally contain much more 
dissolved alkaline constituents per unit of volume in 
dry weather than during floods and periods of full 
flow. The quantity of coagulant must, therefore, 
generally be more carefully watched during high-wa¬ 
ter periods than during dry-weather flow. As has 
been already explained, small upland rivers generally 
contain more suspended matter, per unit of volume of 
flow, during floods than during dry weather, but in 
the case of large lowland rivers the turbidity is often 
more difficult to remove during dry-weather flow 
than during floods; each case must, therefore, be 


THEORY OF RAPID SAND-FILTRA TION. 205 

studied by itself, and the treatment must vary in ac¬ 
cordance with the conditions and requirements. 

The neutralization of the acid, set free by the de¬ 
composition of the sulphate of alumina, changes the 
dissolved carbonates of lime and magnesia to the sul¬ 
phates of the same bases; in other words, the hard¬ 
ness is changed from temporary to permanent; 
generally with the small quantities of chemicals re¬ 
quired for the treatment of water by this process, the 
change of a portion of the hardness from temporary 
to permanent will not be a serious matter. 

Mr. Allen Hazen, in reporting on the filtration of 
the Pittsburgh Water-supply,* places the limit of the 
amount of alum that may safely be used, at ordinary 
periods of flow, at three fourths the amount corre¬ 
sponding to the lime in the water, allowing this 
quantity to be increased about 25 per cent, during 
periods of high turbidity. This increase is per¬ 
missible, owing to the ability of such waters to 
receive a certain amount of chemical without pro¬ 
ducing coagulation, as noted also by Mr. Fuller in 
his Louisville report. 

The quantity of alum required will depend, there¬ 
fore, upon the condition of the water and the results 
desired. In the Providence experiments, Mr. Wes¬ 
ton found one half grain per gallon of water sufficient 
after the filter had reached the stage of effective 
operation; his method of quickly bringing the filter 
to condition was to charge it heavily, before starting, 
with a dose of alum solution, equivalent to 911 grains 


* Report of Filtration Commission, Pittsburgh, 1899 . 





206 


WATER FILTRATION WORKS. 


of sulphate of alumina in one pint of water, and then 
start the filter slowly, bringing it into effective opera¬ 
tion in about half an hour, instead of from one to 
three hours, as required without such dosing. This 
additional dose raised the average charge to about 
0.6 grain per gallon. 

In the Pittsburgh, Cincinnati and Louisville ex¬ 
periments the quantity of coagulant varied princi¬ 
pally with the degree of turbidity of the water. In 
Cincinnati and Louisville the problem of purification 
resolved itself into securing an effluent without tur¬ 
bidity; when this was accomplished the bacterial 
efficiency, and removal of color and other objection¬ 
able qualities, was satisfactory. So far as is known, 
turbidity has no direct effect on the bacterial effi¬ 
ciency of rapid sand-filters; that such efficiency is 
greatest when turbidity is highest is accounted for by 
the fact that the particles of clay causing turbidity are 
themselves very much smaller than the bacteria, and 
a medium that will retain the clay particles will not 
allow the bacteria to pass through. The relation be¬ 
tween turbidity and quantity of chemical required at 
Cincinnati, as given by Mr. Fuller, is shown in Table 
XVII. 

TABLE XVII. 


Turbidity, Parts 
per Million. 

Quantity of Sul¬ 
phate of Aluminum, 
Grains per Gallon. 


Turbidity, Parts 
per Million. 

Quantity of Sul¬ 
phate of Aluminum, 
Grains per Gallon. 

IO 

•75 


150 

2.65 

25 

I.25 


175 

2.85 

50 

1.50 


200 

3.00 

75 

1-95 


300 

3.80 

100 

2.20 


400 

4.40 

125 

2-45 















THEORY OF RAPID SAND-FILTRATION . 207 

These quantities for the Cincinnati conditions 
corresponded to an estimated average annual charge 
of 1.6 grains per gallon of filtered water. During 
freshets the optimum quantity of chemical, according 
to Mr. Fuller, may deviate from the given figures by 
.25 grain. The amount of chemical required, based 
on three days of preliminary subsidence of the water, 
he estimates at from i to 3 grains per gallon for most 
days; occasionally periods might be expected when 
as little as 0.7 grain would suffice,-while during other 
periods much more than 3 grains would be necessary. 

The action of the sulphate of alumina is not lim¬ 
ited, however, to the removal of turbidity and bac¬ 
teria; it possesses the property of combining with the 
coloring matter dissolved in the water, breaking it 
up, coagulating and precipitating it with the sus¬ 
pended matter. This property is very useful in the 
treatment of waters which have acquired a dark color 
from long contact with peat, leaves, grass, roots and 
decaying organic matter. Slow sand-filters, as well 
as those of the rapid type, are almost powerless to 
effect much change in coloring matter of this kind 
unless the water is first treated with sulphate of 
alumina. The alum has also the power of uniting to 
a certain extent with the organic matter in solution 
in the water, and bringing about a higher chemical 
purification than ordinary slow sand-filtration, with¬ 
out the alum, can accomplish. 

Admission of Chemical Solution to the Water and 
Time Necessary for Coagulation and Secondary Subsi¬ 
dence. —In the past the practice has varied much in 


208 


WA TER FILTRATION WORKS. 


regard to the proper time and place for the admix¬ 
ture of the solution of aluminum sulphate. Some 
plants were arranged so that the solution passed into 
the water as it reached the filters, while in others 
some time was allowed to elapse between the admis¬ 
sion of the alum and the filtering of the water. The 
practice must necessarily vary in different works, be¬ 
cause the object of coagulation is two-fold: to reduce 
the amount of suspended matter before it reaches 
the filters, and to catch, in the filter, that which can¬ 
not be economically removed by subsidence. With 
turbid waters, therefore, an economical solution of 
the problem would be obtained by finding that de¬ 
sign for the works in which the combined cost of 
sedimentation, coagulation and filtration would be a 
minimum. It is obviously a waste of money to apply 
a coagulant to a water which contains particles large 
enough and heavy enough to settle out by them¬ 
selves in a reasonable length of time—say 24 hours 
or less. Obviously it also would be a waste of money 
to apply a chemical for the settlement of water con¬ 
taining a high degree of turbidity, partly of fine mat¬ 
ter and partly of coarse, until the coarser had settled 
out unaided. As already shown in Chapter II., rivers 
differ greatly in regard to the character and amount 
of sediment carried in suspension. The economical 
period of subsidence must, therefore, in each case 
be determined by experimental work. In a great 
many plants about 24 hours has been found to be 
the economical limit for the simple subsidence of the 
greater part of the suspended matter, the portion 


THEORY OF RAPID SAND-FILTRATION. 20g 

still remaining in suspension settling at a very much 
slower rate. A portion of this matter still in suspen¬ 
sion, after 24 hours’ subsidence, will be heavy enough 
to go down in a few hours when coagulated with 
other particles. It is apparent, therefore, that a pro¬ 
cess of simple subsidence, followed by coagulation 
and secondary subsidence, will relieve the filters of 
part of the work, saving wash-water, supervision and 
attendance. Another important point, which was 
discovered by Mr. Fuller in Louisville, is that clay 
particles have some faculty of absorbing or holding 
the sulphate of alumina, so that a larger dose of the 
chemical may be taken up by the water than is ac¬ 
counted for by its alkalinity. This is another reason 
for deferring the admixture of the chemical until after 
che employment of plain subsidence to the econom¬ 
ical limit. 

So far as the removal of bacteria is concerned, 
with comparatively clear waters, a long period of 
coagulation does not seem to be advantageous. 
This was exemplified in Weston’s experiments, and 
also in the data given by Mr. Fuller in his Cincinnati 
report. With turbid waters, however, time is of 
considerable significance, a period of from half an 
hour to six hours of subsidence greatly increasing the 
bacterial efficiency. It is absolutely essential that the 
chemical be applied continuously, and in the proper 
proportions, in accordance with the changes in char¬ 
acter and turbidity of the applied water, and in pro¬ 
portion to the amount passing through the filter. 
This is the difficult and delicate part of the process. 


210 


WATER FILTRATION WORKS. 


It requires on the part of the attendants a high de¬ 
gree of intelligence and a conscientious devotion to 
duty. A failure to apply the chemical for a few min¬ 
utes even, under some conditions, might be followed 
by disastrous consequences, which would, in addition 
to the actual inconvenience and danger resulting, 
throw discredit on the plant. 

Mr. Fuller suggests that if, during the stage of 
coagulation and subsidence, the charge of chemical 
be kept a little below the normal, a small additional 
charge may be introduced as the water enters the 
filters, thus economically adjusting the dose to the 
requirements. This is of importance in the mainte¬ 
nance of high efficiency, because with turbid waters 
there is always a tendency to a reduction of efficiency 
for a few minutes after washing. 

With clear waters, judging from the Providence, 
Pittsburgh and Cincinnati experiments, it seems de¬ 
sirable to admit the chemical near the filters. When 
more than an hour was allowed to elapse between the 
time of admission of the solution and the passing of 
the water into the filters the results did not seem to 
be so good. 

Effect of Filtering Medium .—A coarse quartz sand, 
of uniform size of grain, is ordinarily used for rapid 
sand-filters. As the sand serves only the purpose of 
arresting the coagulated suspended matter, it may 
be seen that the finer the sand, within certain limits 
of practicability, the thinner may be the layer, and 
the sooner the filter will reach a normal condition 
in its ability to remove turbidity and bacteria. Of 


THEORY OF RAPID SAND-FILTRATION. 


211 


course, if too fine, clogging will occur immediately, 
and if too coarse too much water will have to be 
wasted after putting the filters in service. The sand 
grains should be as nearly uniform in size as possible 
so that in washing the bed, by reversing the current, 
the particles of sand will not be carried away in the 
wash-water. Incidentally, fine sand offers a greater 
steadying effect to the flow of the water than coarse 
sand, and, therefore, reduces somewhat the proba¬ 
bility of breaks in the top-surface film and the con¬ 
sequent passage of raw water through the bed. More 
water is necessary, however, for washing fine sand 
than coarse; it is also probable that a bed of fine sand 
will require thorough sterilization and washing with 
caustic soda at more frequent intervals than one of 
coarse sand. The usual thickness of bed averages 
about 30 inches, with coarse sands; by using rather a 
fine river sand, however, Mr. Fuller obtained satis¬ 
factory results at Cincinnati with a depth of 20 inches. 

Effect of Rate of Filtration .—Uniform experience 
indicates that the rate of filtration in rapid sand-fil¬ 
ters operated by gravity (providing this rate is uni¬ 
form and feasible in practice) has very little effect on 
the efficiency of the process. In filters of the pres¬ 
sure type, however, the case is entirely different, be¬ 
cause in these very great heads may be suddenly 
thrown on the filters, causing the breaking through 
of the film and a rapid deterioration in the quality of 
the effluent. This weakness of the pressure type of 
filters, as ordinarily constructed, is now so well 


212 


WATER FILTRATION WORKS . 


known that they are now rarely used for the purifica¬ 
tion of drinking waters, being replaced by the open, 
or gravity, type, in which the head cannot exceed a 
certain limit. 

When the pressure filters, however, are located be¬ 
tween the pumps and a large distributing reservoir, 
so that the rate of filtration may be maintained quite 
constant, the pressure type of filter may give very 
satisfactory results. 

At Providence no material difference in efficiency 
was noticeable with rates of from 116,000,000 to 156,- 
000,000 gallons per acre per day. At Cincinnati at 
rates of from 46,000,000 to 170,000,000 gallons per 
acre per day, and at Pittsburgh, with rates from 
68,000,000 to 146,000,000 gallons, no decisive differ¬ 
ences in efficiency were apparent. It was very notice¬ 
able, however, in all these experiments, that the num¬ 
ber of bacteria in the effluents fluctuated with the 
number in the applied water. One point, however, 
of agreement in all recorded tests, is that the rate of 
filtration should not be allowed to change too sud¬ 
denly from a low to a high rate, as such a procedure 
is followed by the breaking loose and washing into 
the effluent of some of the bacteria and matter re¬ 
tained in the filter. Properly designed controllers 
are,therefore, necessary to prevent such fluctuations, 
while the filtered water should be stored in a reservoir 
of sufficient capacity to balance the unequal rates of 
draft. The proper capacity for filtered-water reser¬ 
voirs is discussed in Chapter VIII., and the remarks 
made on page 179 regarding the proper height of the 


THEORY OF RAPID SAND-FILTRATION. 213 

water surface relative to the filters apply equally well 
in the case of rapid sand-filters. 

It is the universal experience that the rate of fil¬ 
tration does not influence the relative amount of 
chemical necessary for proper filtration. Thus, if one 
grain per gallon is necessary for a rate of 50,000,000 
gallons per acre per day, one grain per gallon is suffi¬ 
cient for a rate of 150,000,000 gallons per acre per 
day. 

Effect of Loss of Head .—In operating a filter plant 
as much water should be filtered between washing 
times as possible, due regard being had to economy 
of operation. If washing is put off too long, however, 
the additional amount of water passed at the end of 
the run, per foot of head, will be less than the normal. 
Therefore, the time when washing should be done 
will be indicated when the yield per foot of head 
begins to decrease rapidly below the normal. This is 
an economical question, however, and does not affect 
the efficiency of the process, except indirectly by 
separating, as far as possible, the periods of reduced 
bacterial efficiency due to washing, and thus to a 
certain extent increasing the general average effi¬ 
ciency. 

Mr. Fuller found at Cincinnati that for rates of 
120,000,000 gallons per acre per day, with fine sand, 
the economical loss of head was about 12 feet, and he 
concluded that “ high rates are more economical 
than low ones, and that the full head which can be 
economically used efficiently should be provided. 
Just where the economical limit of the rate of filtra- 


214 WATER FILTRATION WORKS. 

tion is can only be determined from practical experi¬ 
ence with a wider range of conditions than existed 
here, but there seem to be no indications that the 
capacity of a plant originally constructed on a me¬ 
dium-rate basis (100,000,000 to 125,000,000 gallons 
per acre daily) could not readily and economically 
be increased, as the consumption demanded, to rates 
at least as high as the highest tried here (170,000,000 
gallons per acre daily), provided the full economical 
increase in loss of head could be obtained.” 

Negative heads with this process are practicable, 
and, according to Mr. Fuller, desirable if the section 
of greatest resistance is located at the throats of the 
strainers instead of in the sand layer. The liberation 
of the dissolved air, if any, will then occur below in¬ 
stead of in the sand layer where clogging is taking 
place, and it will then not have a tendency to reduce 
the capacity of the filters, as has been the case when 
slow sand-filters were operated under negative heads. 

Effect of Washing Rapid Sand-filters .—Rapid sand- 
filters, after several hours of service, gradually clog 
up so that the yield of filtered water begins to dimin¬ 
ish. When this time comes they are washed by re¬ 
versing the direction of the current of water through 
them, at the same time agitating the sand in such a 
manner that the dirty gelatinous coating on the sur¬ 
face of the filters and on the grains of sand is washed 
off and carried away. It has been observed that 
after washing the number of bacteria in the effluent 
is considerably increased, for a period varying from 
a few minutes to about three hours. It has generally 


THEORY OF RAPID SAND-FILTRATION. 21 5 

been the practice, therefore, to allow the first water 
passing through after washing to run to waste. Mr. 
Fuller, as the result of his Louisville and Cincinnati 
experiments, holds the opinion that where the coagu¬ 
lant is properly applied and the washing is properly 
done, it is unnecessary, at moderate rates of filtra¬ 
tion, to waste any of the water after washing, as the 
reduction of general efficiency following the dis¬ 
charge of this small amount of water not quite so 
good as the average, would not be felt in a large 
plant composed of several units, only one of which, 
perhaps, might be washed at one time. 

After filters have been in service for several 
months their bacterial efficiency generally runs 
down, and even washing will not restore them to 
their best condition. Mr. Weston found at Provi¬ 
dence that after about six months it was necessary 
to wash out the filters with caustic soda in order to 
place them again in a condition of normal efficiency. 

Effect of Trailing .—When filters have been in ser¬ 
vice for several hours, and surface clogging has re¬ 
duced their capacity somewhat, an expedient called 
trailing is sometimes resorted to. This consists of 
scoring the top surface of the sand in concentric rings 
or symmetrical patterns to break the continuity of 
the surface film, and thus increase the yield of the 
filter. The effect of this treatment, as reported from 
the Pittsburgh experiments, if the sand is coarse, 
is to increase the yield, at the expense of puri¬ 
fication, while if the sand is fine the detrimental 
effect, in point of purification, is less noticeable. The 


2l6 


WATER FILTRATION WORKS. 


effect on the yield is not, however, always easy to 
foretell, as with some waters the particles of sus¬ 
pended matter may be carried down so far into the 
filter that surface agitation will not loosen up the 
material enough to increase its permeability. Where 
the particles are coarser and are, therefore, retained 
nearer the top, surface agitation may be more effec¬ 
tive. 





i 






CHAPTER VI. 


THE CONSTRUCTION AND OPERATION OF RAPID 

SAND-FILTERS. 

Up to the present time rapid sand-filter plants 
have been erected by one or another of several com¬ 
panies controlling patents on the processes and on 
the various parts of the different makes of filters. The 
fundamental patent covering the continuous applica¬ 
tion of a coagulant in connection with rapid sand- 
filtration has now expired. 

The city of Louisville, Ky., taking advantage of 
the lapse of this patent, has prepared plans for rapid 
sand-filters of different design from any heretofore 
constructed. 

The various commercial types of rapid sand-filters 
differ from one another principally in the means used 
for adding the chemical to the water, in the strainer 
system for retaining the sand, in the manner of wash¬ 
ing the sand, in the manner of regulating the rate of 
filtration, the method of accomplishing coagulation, 
and the method of admitting the water to the filters. 

Gravity and Pressure Filters .—Rapid sand-filters are 
built of two types, gravity and pressure. As has al¬ 
ready been stated, the gravity type is now used al- 

217 


218 


WA TER FILTRATION WORKS, 


most exclusively for water-supply purification, the 
pressure type being more liable to derangement and, 
unless placed between the pumps and the distributing 
reservoir, less reliable in point of efficiency. The 
pressure type may always find application, however, 
in manufacturing processes where the removal of the 
extremely fine clay particles is not essential. 

In general, the filters are tanks of steel, iron, 
or wood, containing in their bottoms systems of pipes 
for drawing off the filtered water. To prevent the 
sand from escaping with the water, strainers of brass- 
wire cloth of fine mesh, brass plates or cones bored 
with small holes, or slotted plates or rosettes, have 
been employed. The sand layer is usually from about 
two and a half to three feet thick ; the sand is of rather 
coarse grain, quite uniform in size, and the piping is 
so arranged that the water may be admitted to the 
top of the filter and taken away, after filtration, from 
the bottom. Overflows are also provided, in the 
gravity type, as well as a connection by which the 
fitered water may be forced back through the filter 
for washing the sand. Arrangements are also made 
to permit the wasting of the water, upon placing the 
filter in operation after washing, until the surface film 
has again formed. The washing arrangements, in the 
gravity type, generally consist of arms, or rods, that 
can be lowered down into the sand. The rotation of 
these arms, combined with the upward motion of the 
wash-water through the sand, loosens up and scours 
off the deposits of dirt and coagulant which have 
formed around and between the sand grains. Other 


RAPID SAND-FILTERS. 


219 


methods of washing are described on subsequent 
pages. 

In the plans for the Louisville plant the filters, in¬ 
stead of being in small circular units, are rectangular 
and comparatively large in area. They have sides and 
bottoms of concrete instead of sheet metal or wood. 
The bottoms also, instead of having a system of pipes 
and strainers for carrying away the filtered water, 
have layers of brass-wire cloth supported on a frame¬ 
work of iron in such a manner as to form a hollow 
floor under the whole filter area. 

A perspective view showing the construction and 
arrangement of a Jewell subsidence gravity filter is 
shown in Fig. 37. In this type of filter the in¬ 
fluent water enters the subsidence tank in a direction 
tangential to the periphery, in order to give a 
rotary motion to the water in the tank, by which the 
speed of coagulation may be hastened. The water is 
admitted upon the surface of the sand through the 
central vertical pipe, and is drawn off after passing 
through the sand through the delivery valve, 5. 
After passing through the controller, 7, it goes to the 
filtered-water reservoir. The filter is washed by 
revolving the rakes or agitators, at the same time 
forcing filtered water upward through the strainer 
system, by closing valves 1, 2, 6, 3 and 5, and 
opening valve 4. After the washing has been com¬ 
pleted, valve 4 is closed and valves 1 and 3 are 
opened, permitting the filtered water to run to waste 
until the filter is again in the proper condition. 

Filters of this type are in use, among other places, 


220 


WATER ElL TEA T ION WORKS. 


in the recently completed plant at East Albany, N. Y. 
A photographic view of the interior of this plant is 
given in Plate XV. 



Fig. 37* —Sectional View of a Jewell Subsidence Gravity 

Filter. 


In the Continental filter, which is shown in Figs. 
38 and 39, the washing is done by compressed air and 





























































































































































































































Plate XV. —View of the Interior of the East Albany, 

Filter Plant. 




































RAPID SAND-FILTERS. 


223 


wash-water used alternately. Other features of this 
design are the covering of the strainer system with a 
layer of gravel, and the distribution of the raw water 
over the surface of the sand by a trough extending 



Fig. 38. —Plan of a Continental Gravity Filter with 

Air Wash. 

around the inner edge of the filter and out over the 
top of the sand in the shape of a cross, in order to 
distribute the water evenly over the sand at a very 
low velocity. 

The New York sectional wash gravity filter is 
shown in Fig. 40. I11 this type of filter the central 

















































































224 


WATER FILTRATION WORKS. 


valve is so designed that the wash-water may be 
forced through only one section of the filtering sand 
at a time. By this means more thorough scouring 
of the sand grains is accomplished than if the whole 
filter were washed at once. The water is admitted to 



Fig. 39. —Sectional Elevation of a Continental Gravity 

Filter with Air Wash. 

the filter through a set of perforated pipes supported 
above the sand level. In Fig. 41 is shown the New 
York sectional wash pressure filter. 

There are several other makes of rapid sand-filters 
in use for the filtration of municipal water-supplies, 
but the general principles underlying the design of 
such are sufficiently well illustrated in the types above 
described. 












































































































































































































































































































RAPID SAND-FILTERS . 


225 


Introduction of Chemical Solution .—The sulphate of 
alumina should be of a high grade, as the slight 
economy resulting from the use of low grades is not 
warranted by experience. Customers frequently buy 
the sulphate on the basis of the amount of AL 2 O s it 



Fig. 40.—Sectional View of a New York Sectional-wash 

Gravity Filter. 


contains, the usual proportion being about per 
cent. Grades containing as low as 12 per cent, have 
been used successfully, but in these the insoluble 
compounds, mostly silicates, tend to foul the pipes 
and orifices, making their cleansing necessary more 














































226 


WATER FILTRATION WORKS. 


frequently than if a high grade were used. The mix¬ 
ing tanks are generally of wood, of sufficient capacity 
to hold six hours’ supply of the solution. The 



requisite quantity of alum is placed in a crate or box 
near the top of the tank, and a small stream of water 
is sprayed upon it, percolating down through the 
alum and falling into the tank. The flow of the 





















RAPID SAND-FILTERS. 


227 


stream can be so regulated that by the time the tank 
is filled the alum will all be dissolved. The solution 
is kept in agitation by stirring with mechanical de¬ 
vices, or by compressed air forced up through the 
bottom. Two tanks should be provided so that the 
solution may be in preparation in one while being 
drawn from the other. The alum solution goes from 
the solution tanks to the measuring tank, from which 
it in turn flows into the filter inlet pipe. A typical 
measuring tank, for use with gravity filters, is shown 
in Fig. 42. The depth of the solution over the ori- 

l 



Fig. 42.—Section of a Typical Alum Solution Measuring 
Tank for a Gravity Filter. 

fice in the bottom of the tank is kept uniform by pro¬ 
viding an overflow through which the surplus may 
flow back to the solution tanks. If the solution 
flows to the measuring tank by gravity, the overflow 
is pumped back to the solution tanks. The dose of 
the solution is varied, in accordance with the char- 
































228 


WATER FILTRATION WORKS. 


acter of the water, by changing the size of the orifice 
or by changing the strength of the solution. 

A type of measuring tank for use with pressure 
filters is shown in Fig. 43. In operation this tank is 
first filled with a known quantity of potash alum. 



Fig. 43.—Section of an Alum Solution Tank for a Pressure 

Filter. 

A small stream of water is then admitted through the 
inlet. The water passes down through the alum, 
dissolving it, and then up through the outlet 
pipe and into the influent pipe to the filter. 
The pressure required to cause this flow is about -J 
lb. per sq. inch above the pressure as the water enters 
the filter. This is produced by throttling the influent 
pipe between the two connections with the tank. 
An apparatus is sometimes used in connection with 
this tank, to vary the dose of solution in proportion 
to the flow of water to the filter. Great accuracy, 
however, is not claimed for such regulation. 



















RAPID SAND-FILTERS . 


229 


In large gravity plants the addition of the chemical 
solution may conveniently be accomplished (as pro¬ 
posed for the Little Falls plant for the East Jersey 
Water Co.) by providing a plate in the bottom of 
the measuring tank, the plate having an orifice for 
each filter, and each orifice having the same area as 
the others. By having several of these plates, the 
orifices in each plate having a different area from 
those in the others, the dose of chemical may be 
varied in accordance with the character of the water. 
Further regulation of the dose may be accomplished 
by having the solution made up in one, two, three or 
four per cent, mixtures, and thus save multiplication 
of plates. If a filter is out of service an orifice is 
closed and the dose of chemical will thus always cor¬ 
respond with the amount of water going to the filters. 

In place of having a gravity feed the chemical so¬ 
lution is sometimes pumped into the influent pipe. A 
successful pump for this purpose is illustrated in Fig. 
44. A small propeller wheel is mounted in a section 
of the influent pipe, and a bevel-gear wheel on the 
shaft of the propeller turns a small shaft which car¬ 
ries the crank driving the pump. The pump is made 
of hard rubber and is mounted on the pipe. The 
chemical solution is drawn from the solution tank 
by the pump, and forced into the influent pipe. This 
apparatus must work very freely in order to be suc¬ 
cessful; in fact its work should be limited merely to 
measuring the quantity of solution. It is also neces¬ 
sary to restrict the section of the influent pipe so 
that the velocity at the propeller will be at least six 


230 


WA TER FILTRATION WORKS. 


feet per second, otherwise the velocity head will not 
be sufficient to work the apparatus. The pump 
should always be kept very clean, and therefore a 



Gravity or a Pressure Filter. 

high grade of sulphate of alumina is desirable when 
this apparatus is to be used. This system of chem¬ 
ical feed may be used with either the pressure or 
gravity type of filter. 

All the piping in connection with the chemical feed 



















































































































































































RA PID SA ND-FIL TERS. 2 31 

should be of brass or of lead. Lead pipe gives less 
trouble with clogging than brass, and its length of 
life is also greater, the brass pipes lasting about ten 
years. 

Regulating Apparatus .—The controller designed by 
Edmund B. Weston, C.E., is shown in Fig. 45 and 
is described by him as follows:* 



Fig. 45.—Section of Weston’s Automatic Controller. 

“The necessity of an automatic controller for 
measuring the flow through a filter-bed and keeping 


* The Norfolk, Va., Filter Plant. Paper by E. B. Weston read 
before 20th Annual Conv. Am. Water-works Association, at Rich¬ 
mond, Va., May 16, 1900. 

































































































232 WATER FILTRATION WORKS. 

it perfectly constant during - the process of filtration, is 
of the utmost importance. 

“ The two principal reasons for the necessity of an 
accurate controller are: 

“ 1st. The exact quantity of water passing through 
the filter-bed being known, the correct quantity of 
sulphate of alumina solution can be accurately and 
uniformly applied to the raw water, by gravity or 
other means. 

“ 2d. By keeping the flow of water through the 
filter-bed perfectly constant, scouring action in the 
filter-bed is avoided. 

“ The controller is connected (outside of the filter) 
to the draft or delivery pipe of the filter, from which 
the filtered water passes through butterfly valves in 
the lower part of the controller. The controller con¬ 
tains a float mounted on a hollow float-stem, operat¬ 
ing in guides at the top and bottom of the controller. 
Beneath the float is a deflector, designed to quiet the 
incoming water and reduce any currents, thereby giv¬ 
ing a smooth entrance to the discharge tube, and be¬ 
ing aided in this respect by the flaring ring at the top 
of the discharge tube. Mounted also upon the float- 
stem at a fixed distance below the float, so as to be 
maintained at a constant depth, is a disc which is 
turned with a thin edge and sharp corners and of such 
a diameter as will give the annular orifice, between 
the disc and the walls of the discharge tube and which 
rises and falls with the float, a predetermined area 
proportional to the desired rate of discharge. The 
float being mounted at a fixed distance from the disc, 


RAPID SAND-FILTERS. 


233 


thereby maintains a constant head of water upon the 
movable annular orifice. The inlet butterfly valves 
in the lower part of the controller are operated by 
levers connected to the float, so that the rise and fall 
of the latter tends to close and open them. 

“ The regulation of the flow of water through the 
filter-bed may be described as follows: With a given 
head of water upon the surface of the filter-bed and 
a free discharge from the filter, the rate of discharge 
will vary with the condition of the filter-bed. If, for 
a given level of water in the controller, the head on 
the inlet pipe be such that more water will pass 
through the inlet butterfly valves than can be dis¬ 
charged through the annular orifice, the level of the 
water in the controller will rise, and with it the float, 
which will tend to close the inlet butterfly valves and 
throttle the flow so that equilibrium is established 
between the supply to and the discharge from the 
controller. If, on the other hand, the head on the in¬ 
let pipe be reduced, and consequently the flow 
through the butterfly valves, the water level in the 
controller falls and the float falling with it increases 
the opening of the valves and thus restores the 
equilibrium. Should the head on the inlet pipe be 
reduced below that determined by the minimum 
limit, the water level in the controller will fall below 
the minimum limit, the float will be submerged less, 
and consequently the head on the annular orifice and 
discharge tube will be diminished below the minimum 
desired. This will indicate a needed washing of the 
filter-bed, which is manifested at Norfolk by an indi- 


234 WATER FILTRATION WORKS. 

eating- water gauge, that is actuated by a float in a 
vertical pipe which is connected to the inlet pipe of 
the controller. The rated capacity of discharge may 
be adjusted by altering the depth of submergence of 
the disc, or by changing the area of the annular ori¬ 
fice by substituting a disc of different size. Air is ad¬ 
mitted below the disc through the hollow float-stem, 
which has vents below the disc. 

“ Tests have been made with this design of con¬ 
troller under heads ranging from 0.33 to 18 feet, and 
have not shown any practical measurable variation 
in the discharge.” 

Washing Arrangements .—In many of the existing 
filter plants it is difficult to wash the sand near the 
bottom and between the strainers, and the more or 
less polluted water in this unwashed sand is apt to af¬ 
fect the quality of the effluent. The floor of the 
Louisville filters is designed to correct this by per¬ 
mitting all parts of the area to be washed alike. 

The stirring arms for the Louisville plant will be 
mounted on a travelling platform suspended over the 
beds on rollers, and capable of being raised or low¬ 
ered or transported sidewise. This will permit one 
apparatus to serve the filters of the whole plant. 

In Plate XVI is shown the agitator used in the 
Jewell filter at the Pittsburgh experiment station. 
The rods are pivoted to the arms in such a manner 
that when revolving in one direction they will stand 
vertically and stir up the sand. When revolved in 
the reverse direction they assume an inclination of 
about 60 degrees from the vertical, so that their ends 


Plate XVI.— Agitator of Jewell Filter. Pittsburgh Experiment Station. 










RAPID SAND-FILTERS. 


237 


rest upon the surface of the sand. A short chain is 
attached to the end of each rod, as may be seen in 
Fig. 37 - 

The agitator used in the Warren filter is shown 
in Plate XVII. The stirring rods in this apparatus 
are movable vertically by a hydraulic lift supported 
above the filter. 

In large plants the filters may be washed by forc¬ 
ing air upward through the sand-bed. The air is de¬ 
livered at the filters under a pressure of about 3 
lbs. per square inch, by rotary blowers. On reach¬ 
ing the strainers the air expands and lifts the bed of 
sand and superincumbent water sometimes to a 
height of two or three inches. The bubbles of air 
carry the sand grains upward with considerable 
force, rubbing them together, scouring them quite 
effectively, and floating them about through the en¬ 
tire depth of water above the sand. Mr. Charles L. 
Parmelee, Chief Engineer of the New York Con¬ 
tinental Jewell Filtration Company, has seen grains 
of sand thrown into the air above the surface of the 
water, by bursting bubbles, when the water stood six 
feet in depth over the normal sand surface. 

Air-washing has been in use since 1896 in pres¬ 
sure filters, and since 1898 in filters of the gravity 
type, and is said to be as effective as the agita¬ 
tion of the sand with rakes, combined with the usual 
water-washing process by reversal of current. 

In washing with air the air and wash-water are 
used alternately. If the air and water are used to¬ 
gether considerable sand will be carried away with 


238 wA TER FILTRATION IVOR NS. 

the wash-water. The amount of power required for 
air-washing is said to be about the same as for agita¬ 
tion with rakes, but the amount of wash-water re¬ 
quired is about half as much with air as with the 
rakes. 

The air system, however, on account of the ex¬ 
pense of installation, is not used in small plants. Its 
chief advantage in large plants comes from permit¬ 
ting the use of rectangular filters. 

Air-washing in large plants is now considered 
quite satisfactory. Its use has been recommended in 
the large filter plant, for which plans were recently 
prepared, to be erected at Little 'Falls, N. J. 

Cost of Rapid Sand-filters .—Data on the cost of ex¬ 
isting rapid sand-filter plants are not valuable for 
comparisons, because of the included values of patent 
rights and other expenses incident to the business of 
private companies. With the expiration of the funda¬ 
mental patent, however, it becomes a simple matter 
to design a plant and estimate its cost. In the general 
run of large plants, with circular filters, the cost has 
been at the rate of probably about $500,000 per acre 
of filter surface, excluding the cost of buildings, foun¬ 
dations, pumping machinery, land, etc., or, in other 
words, they have been about ten times as expensive 
as covered slow sand-filters of the same area. As, 
however, the rapid sand-filters pass the water at a 
rate many times faster than the slow filters, the rela¬ 
tive cost of construction, per unit of water filtered, is 
really only about from one third to one fifth as great 
for the rapid as for the slow sand-filters. With im- 


Plate XVII.—Agitator of Warren Filter. Pittsburgh Experiment Station. 

239 








RAPID SAND-FILTERS. 


24I 


provements in design, in the matter of larger units, 
steel and concrete construction, economy of space 
and piping resulting from the use of rectangular 
filters, improvements in sand-washing devices, etc., 
the cost of construction and of operation of rapid 
sand-filter plants may be brought still much lower. 
Cheapness of installation and efficiency, combined 
with economy in operation, are the greatest points to 
attract favorable attention. When improvements, 
along the lines suggested above, have been perfected, 
there is no doubt but that rapid sand-filters will find 
a more extensive field of application in the future 
for the purification of drinking waters. 

When constructed in small circular units they also 
offer an advantage in another direction, which was 
first noted in Philadelphia, in the report of the 
Mayor’s Expert Water Commission. A filtered sup¬ 
ply from the Schuylkill and Delaware Rivers was 
recommended. The Schuylkill, on account of its 
small flow, could not be depended upon to furnish 
sufficient water for supplying the entire district 
through which it passed, when, in the future, the 
population should increase beyond a certain limit. 
As the filter plants in the upper portion of the city 
would always have to depend on this stream for wa¬ 
ter, it was recommended that the one lowest down¬ 
stream be made a rapid sand-filter plant composed 
of small units, so that in the future, when all 
the water of the river was needed for the upper 
plants, the lower site could be abandoned and the 
filters be moved over to the Delaware River. This 


242 


WATER FILTRATION WO RES. 


plan would entail less loss than the abandonment of 
an expensive slow sand-filter plant. 

Operation .—The water after having been treated 
with the coagulant from the supply tank, by means 
of an automatic feed which secures the delivery of 
a quantity of alumina in proportion to the amount 
of water entering the filter, passes into the settling 
basins where coagulation takes place and a certain 
amount of the suspended matter may be precipitated. 
An energetic agitation of the water, after adding the 
chemical solution, materially hastens the process of 
coagulation, thereby permitting the use of smaller 
settling basins. 

When a filter is clean the resistance to the 
passage of the water through the sand layer is much 
less than after it has been in service for a while and 
the rate of filtration, with a constant head, would, 
therefore, gradually decrease. In other words, at 
first it would filter the water too rapidly. In order 
to regulate this speed, automatic devices, called con¬ 
trollers, have been devised. These regulate the 
speed to a predetermined rate, thus making the ac¬ 
tion of the filter regular and uniform. After the 
available head has been used up the filter must be 
washed. The controller devised by Mr. Edmund B. 
Weston has already been described. 

Period of Time Between Washings ._—The length of 
time between washings, at the Cincinnati experi¬ 
mental plant, with fine sand in the filters, ranged 
from 8 to 24, and averaged 15 hours, while with the 
coarse sand these periods became 6, 36 and 20 


RAPID SAND-FILTERS. 


243 


hours, respectively. The general average for several 
plants of which the author has secured records 
seems to be about 16 hours. The coarse sand in the 
Cincinnati experiments could be washed in about 20 
minutes, while the fine sand required 30 minutes. 
In Mr. Weston’s Providence experiments the aver¬ 
age time of washing was about 11 minutes, and the 
water was wasted for 30 minutes after washing. At 
the Pittsburgh Experiment Station the quality of the 
effluent was below the standard for about 20 min¬ 
utes after washing, and it was, therefore, found ad¬ 
visable to waste about 2 per cent, of the filtered 
water. 

Lost Sand .—A certain amount of sand, depending 
upon the judgment of the operatives, the fineness 
and uniformity coefficient of the sand and the veloc¬ 
ity of the wash-water, will be wasted or lost in wash¬ 
ing the filters. An allowance of about 3 inches in 
depth, per annum, would probably not be excessive 
with such sands as are commonly employed. The 
lower the uniformity coefficient the less will be the 
loss from this cause. 

Labor for Operation .—The labor necessary for 
operating a rapid sand-filter plant is a small part of 
the cost of operation, varying from 12 to 20 per 
cent., usually, of the total cost. In a plant in one of 
our southern cities having 22 pressure-filters, with 
a daily average capacity of 3,000,000 gallons, the 
filters are run by two men at salaries of $60 and $40, 
respectively, per month. For a larger plant, say of 
50,000,000 gallons daily capacity, the force would 


244 


WA TER FILTRATION WORKS . 


probably consist of three shifts of engineers and 
firemen and three shifts of laborers of four to 
each shift. The same force could take care of a 
larger plant. A plant of 100,000,000 gallons daily 
capacity could probably be run with three shifts of 
engineers and firemen and three shifts of laborers of 
six to the shift, providing the filters did not require 
washing oftener than once in eight hours, could be 
washed in 30 minutes to the filter and were in 
units with a daily capacity of not less than 1,000,000 
gallons each. 

Wash-water .—The normal rate for operating rapid 
sand-filters is from about 100,000,000 to 150,000,000 
gallons per acre daily, the filters being allowed to run 
until they become so clogged that the allowable loss 
of head is consumed. As already stated, they are 
washed by pumping or forcing filtered water back 
through the underdrains at a rate from three to four 
times as great as that at which the filters operate 
normally, at the same time agitating the sand beds 
with revolving arms. They are also sometimes 
scoured by sectional washing, or by using com¬ 
pressed air and wash-water alternately. The quan¬ 
tity of wash-water required will depend upon the 
size of the grains of sand, the character of the 
raw water and the amount of clogging. At Cin¬ 
cinnati, Mr. Fuller found that from 4 to 9, and 
averaging 5 per cent, of the filtered water was 
required for washing with the fine sand, while from 
2 to 6, and averaging 3 per cent, was needed with 
the coarse sand-filters. In the Providence experi- 


RAPID SAND-FILTERS . 


245 


ments Mr. Weston found that 4.9 per cent, of the 
filtered water was needed for washing the sand and 
that it was necessary to waste about 2.9 per cent, on 
starting the filters in operation after washing. Mr. 
Fuller, in his Cincinnati report, states that with 
proper manipulation no wastage of wash-water was 
necessary, as it could be pumped back into the sub¬ 
siding reservoir, where the great bulk of the bac¬ 
teria and suspended matters would be deposited by 
plain subsidence in less than one day. He also states 
that although the quality of the filtered water was 
inferior to the normal directly after washing the fil¬ 
ters, the evidence indicated that in a large plant it 
would not be desirable or necessary to waste any 
filtered water. 


CHAPTER VII. 

CONCLUSIONS. 

General .—Leaving out the question of household 
filters, which has no place in a work of this charac¬ 
ter, we are now in a position to summarize the 
knowledge thus far gained by experience with the 
purification of water by filtration on a large scale. 
Generally speaking, there are only two principles upon 
which municipal filter-plants have been successfully 
designed in this country. In one type the water is 
filtered slowly, through beds of sand, without the 
use of chemicals to aid the process; in the other the 
water is filtered rapidly through beds of sand after 
a coagulating material has been introduced into 
the water. In slow sand-filters the most usual rate 
of filtration is about 3 million gallons per acre per 
day; in other words, the water passes down through 
the sand in a coumn having the full area of the fil¬ 
ter and a depth of about ten feet. In rapid sand- 
filters the rate of filtration is from 30 to 50 times as 
fast. The slow type is suited for the purification of 
polluted waters not too highly colored by vegeta¬ 
tion and not carrying too great an amount of finely 
divided suspended matter. The rapid type is more 
suited for the removal of turbidity and color; when 
carefully operated rapid sand-filters can give a very 

high efficiency, but sufficient experience has not 

246 


CONCLUSIONS. 


247 


yet been had to warrant the unqualified statement 
that they are ordinarily as safe as the slow filters, in 
the treatment of a sewage-polluted water. Operating 
at high rates, a break in the regularity of manage¬ 
ment would be likely to cause a great degree of de¬ 
terioration in the effluent; and further, filters of the 
rapid type are not suitable for the economical treat¬ 
ment of very soft waters. 

There are undoubtedly situations where a combi¬ 
nation of slow and rapid sand-filters would prove 
economical, for instance, near the line of latitude 
where is it doubtful whether or not it would be eco¬ 
nomical to cover the filters. In such places a com¬ 
bined plant, if circumstances permit, might work out 
satisfactorily. The rapid filters could be relied upon 
mostly in cold and the slow ones in warm weather, 
each serving at the period of the year when the con¬ 
dition of the water, as to pollution, is best suited for 
the respective type, thus saving the cost of roofing 
over the slow sand-filters. The relative areas of slow 
and rapid filters would have to be determined from 
a special study of the prevailing meteorological con¬ 
ditions. A combination of slow and rapid sand-fil¬ 
ters would not prove of benefit in the clarification of 
turbid waters, because while first passing through 
the rapid filters the coagulant would abstract finer 
matter from the water than could be removed sub¬ 
sequently in the slow filters; but in the case of a 
very highly polluted water double filtration, first 
through rapid, and then, after aeration, through slow 
sand-filters, the essential conditions for the proper 


248 WATER FILTRATION' WORKS. 

action of the two processes being always kept in 
view, might be preferable to double filtration through 
slow sand-filters, as has been sometimes recom¬ 
mended. With a turbid, sewage-polluted water condi¬ 
tions might sometimes arise that would make it advis¬ 
able to use sedimentation and then slow sand-filtra¬ 
tion, finishing with rapid sand-filtration in order to 
remove the last traces of turbidity. Where the water 
is occasionally too turbid, or contains too much color 
to be successfully treated by slow sand-filtration, but 
still ordinarily is of suitable character for treatment 
by this process, it may be necessary, at times, to pre¬ 
cede filtration by sedimentation, with, or, perhaps, 
without, the aid of a coagulant. 

The essential condition for the satisfactory and 
safe operation of the rapid type of sand-filters is that 
the dose of coagulant be continuously and properly 
applied. This necessitates the occasional, or, in some 
cases it might be more properly said, constant ex¬ 
amination of the raw water for turbidity and alka¬ 
linity. A failure to apply a sufficient amount of 
chemical would be followed by reduced bacterial 
efficiency, and an overdose might be followed by the 
acidulation of the water with its attendant evils of 
corrosion in the street-mains and service-pipes. For 
this reason it is evident that the rapid type is better 
suited for large cities, where the plant would be of 
sufficient extent to afford the constant services of a 
competent chemist, than for cities too small to afford 
chemical supervision. Of course, in some places, 
where removal of turbidity is the only object, the ser¬ 
vices of a chemist could be dispensed with if stand- 


CON CL US 10 NS. 


249 


ards of turbidity and the accompanying quantity of 
chemical solution were once established; but in waters 
polluted with sewage, and varying in alkalinity at dif¬ 
ferent stages of flow and periods of the year, safety 
from one extreme or the other can only be assured 
with the services of a chemist. 

On the other hand, the slow sand-filters do not 
generally require such careful attention. If the 
regulating apparatus is properly designed, so that 
the filters cannot be operated at too high a rate, 
there is little concerning the efficiency of the filters 
that will depend upon the faithfulness of unskilled 
laborers. 

The cost of installing a covered slow sand-filter 
plant, to filter a given quantity of water daily, is from 
three to five times as great as the cost of a rapid sand- 
filter plant of the same capacity. The annual cost 
of operation, however, is about the same, the cost of 
the chemical solution, and greater allowances for 
deterioration, making up for the lower interest 
charges in the case of rapid sand-filters. 

A few words concerning certain methods of water- 
filtration in use in foreign countries seems to be 
appropriate at this point. 

The Anderson Process .—The Anderson process of 
water-purification, which has found considerable ap¬ 
plication in Europe, is somewhat akin in principle 
to the process of rapid sand-filtration. The process 
consists of the filtration of the water through beds of 
sand after a coagulant has been introduced into the 
water. This coagulant is ferric hydrate, produced 
by agitating filings and chips of iron in the water. 


250 


WATER FILTRATION WORKS. 


Some of the iron is'taken up in solution, and after¬ 
ward, on exposure to the air, again passes out of solu¬ 
tion in an insoluble flocculent form; this is re¬ 
moved, together with the other impurities, by 
sedimentation and filtration. The first large An¬ 
derson plant was built at Antwerp. Later plants 
have been installed at Choisy-le-Roi, near Paris, and 
at Boulogne-sur-Seine. The objects of using the 
coagulant are to remove turbidity and reduce the 
area necessary for filtration. The iron process 
is not of use for removing the stain due to 
dissolved peaty matter, because the iron will form 
a soluble compound with the organic constituents 
of the coloring matter. Aluminum sulphate has 
been found to be the best chemical for this purpose. 

Pasteur-Chamber land Filters .—The best-known 
porcelain or artificial-stone filters are the Pasteur 
and the Fischer, or Worms, filters. The Pasteur fil¬ 
tering medium consists of hollow unglazed tubes of 
porcelain through which the water is forced. The 
grain of the porcelain is so extremely fine that the 
bacteria are retained on the surface of the tubes. A 
Pasteur plant of considerable size has recently been 
installed for the municipal supply of Darjeeling, 
India. 

Worms Filter .—The Fischer, or Worms, filters 
are similar in principle to the Pasteur, in that they 
depend upon the surface of the filtering medium for 
the retention of the bacteria, without the action of 
a coagulant or of the nitrifying organism. The 
slabs of artificial stone, through which the water is 
passed, are made of sand, silicate of lime and soda. 



Plate XVIII.— Fischer or Worms Plate, ready to be placed in the Filter 

Pittsburgh Experiment Station. 

251 













;^4 


*4 


■ 

. 













































CON CL US IONS. 


255 


moulded into squares about 3^ feet on a side. They 
are placed in pairs, with their concave sides together, 
and the water filters through to the inside space, 
while the dirt is left on the outside. They are 
cleaned by forcing steam through them in the re¬ 
verse direction. The largest cities using these fil¬ 
ters are Worms-on-the-Rhine and Arad, Hungary. 

There are numerous other filters of this type, but 
so far as the writer knows none of them has been 
used for municipal supplies. Both the Pasteur and 
Fischer types of filter can produce good results in 
the filtration of waters of certain kinds, but it is not 
settled that they are practicable of installation in the 
United States, because of cost of construction, cost 
of operation and lack of sufficient experience with 
them to determine, in the treatment of our waters, 
their durability and the cost of replacing breakage. 
In Plate XVIII is given a view of a Fischer plate 
ready to be placed in position in a filter at the experi¬ 
ment station at Pittsburgh, Pa. An idea of the con¬ 
struction of these plates may be gained from Plate 
XIX, which shows two units broken at the same 
station. 

Regarding the Maignen filters, in which a layer 
of asbestos is spread over the surface of the sand, 
it is sufficient to say that at the present time the 
system is not in use in the United States for the 
purification of a municipal water-supply. 

It is hoped that when these different processes may 
have been tried on a large scale in this country the 
results of such trials may be recorded in future edi¬ 
tions of this work. 


CHAPTER VIII. 


FILTERED-WATER RESERVOIRS. 

Location .—When the filtered-water reservoir is to 
be near the filters it should be located in a position 
to which the water from all the filters may be con¬ 
ducted with the minimum length of piping. It 
should also be constructed, as stated on page 179, 
at such an elevation that the highest water level can 
not limit the filtration head. 

Shape .—Reservoirs are usually made rectangular 
in plan when the topography of the ground does not 
require another shape. Circular or polygonal reser¬ 
voirs are more difficult to roof than the rectangular 
type, and hence are rarely chosen when the rect¬ 
angle is possible. While the quantity of masonry 
in the side-walls in such is less than in any other 
shape, the constructional details of roofed reservoirs 
may counterbalance this advantage. An example of 
the covered circular type is to be seen at Arnheim, 
where the vaulted roof is carried on iron posts and 
girders. 

The reservoir should be divided into two or more 
independent basins by heavy cross-walls. Gates con¬ 
trolling openings through these cross-walls will fur- 

256 



FILTERED-WATER RESERVOIRS. 2$7 

nish communication between the different basins. 
Each basin should have an independent junction 
with the inlet pipe for filtered water, with the 
outlet pipe, and also with the overflow and drain 
pipes. 

Circulation .—To prevent the water in the reser¬ 
voir from becoming stagnant, caused by some of 
it not being able to escape from the remote cor¬ 
ners, the expedient is sometimes adopted of dividing 
the reservoir by partition walls into a number of nar¬ 
row parallel channels, each connecting with the next 
at alternate ends, thus compelling all the water to 
move in a continuous direction toward the outlet. 
The filtered-water reservoirs at the Lake Mueggle 
works, Berlin, are built in this way, and also the large 
reservoir for spring-water at Frankfort-on-the-Main. 

Capacity .—In very many of the European filter 
plants the filtered-water reservoir is too small to 
have any effect as a balancing reservoir; the com¬ 
pensation for hourly and daily fluctuation being 
made by operating the filters at a higher rate to 
meet the demand. It is needless to say, however, 
that such a practice, unless properly understood and 
carefully watched, is not conducive to high efficiency. 
With clear waters, nearly free from bacteria in their 
natural state, the danger of reduced efficiency by in¬ 
creasing the rate abnormally is much less than with 
water more polluted, and, therefore, with compara¬ 
tively pure waters the storage may be less than with 
polluted waters. 

The capacity of the filtered-water reservoir at 


258 


WATER FILTRATION WORKS . 


Hamburg is about 6.2 per cent., and at Berlin (Lake 
Mueggle)about 5.6 per cent, of the average maximum 
daily draft. Since water even after very careful fil¬ 
tration still contains a small number of bacteria 
which have passed through the filter, and also a 
small amount of food matter, it is essential that it 
should be delivered to the consumer as soon as possi¬ 
ble in order that its quality may not deteriorate by 
the growth of these micro-organisms during storage. 
This consideration indicates the desirability of a 
small reservoir. On the other hand, if the filtered- 
water reservoir is to provide the only storage, a cer¬ 
tain amount of reserve is desirable in case of fires, 
unless a separate supply is provided for that purpose, 
or a by-pass arranged so that in such an emergency 
the unfiltered water can be turned directly into the 
mains. This plan, where the water is treated more 
to remove turbidity or color than specific bacteria 
of contagious diseases, is often feasible. Some au¬ 
thorities contend that the plan is safe in all cases, 
because the infection likely to arise from such occa¬ 
sional delivery of raw water will be less than the 
total infection resulting from the secondary growth 
of the bacteria in large filtered-water reservoirs. 
This is still, however, one of those points which can 
never be definitely settled so far as moderately pol¬ 
luted waters are concerned. It is, however, very de¬ 
sirable to have the storage sufficient to balance the 
hourly fluctuations in consumption, and for Ameri¬ 
can conditions this will require a reservoir capable of 
holding about 30 per cent, of the average daily draft, 


FIL TER ED- IVA TER RESERVOIRS. 259 

presuming that the filters have sufficient area to de¬ 
liver the maximum daily draft without exceeding the 
maximum rate of filtration established for them. 
This is about a seven hours’ supply at the average 
daily rate; Professor Burton recommends about ten 
hours’ supply as a minimum, in addition to a fire re¬ 
serve, expressed by the empirical formula: 

Minimum cubic feet of storage for fire re¬ 
serve should be about 200 times the square root 
of the number of inhabitants served. 

The proper allowance for fire reserve for Amer¬ 
ican conditions must be determined by a special 
study. Should there be a large distributing reservoir 
in the system it should be taken into account in the 
designing of the filtered-water reservoir, and the 
combined capacity of the two should be sufficient, at 
least, to balance the daily and hourly fluctuations of 
draft and provide the proper reserve for fires and for 
accidents to the machinery. See also page 108. 
Frequently, as in the Berlin and Hamburg plants, 
other reservoirs are provided in the system, and the 
capacity of the small reservoir at the works need not 
then be over from 5 to 7 per cent, of the daily mean 
supply, and the rest of the storage may be provided 
for at other points. 

The most economical shape for a rectangular cov¬ 
ered reservoir, if not subdivided, is the square. If 
divided into two basins by a partition wall costing 
about as much per foot run as the side-walls, the 
length of the short side of each basin should be 
three fourths the length of the long side. For any 


26 o 


WATER FILTRATION WORKS. 


other number of basins the formulas given on pages 
115 and 117 may be used. 

Depth .—Since the relative amounts and costs of 
excavation and masonry vary with the depth of a 
reservoir, it is evident that there is one depth which 
will be less expensive than any other. For unroofed 
square reservoirs, without partitions, the most desir¬ 
able depth can be found approximately, according to 
Prof. Friihling,* by the following formula: 

, 5 /£?0' + * f + w ) 2 
V 3 6w 2 

If divided by a partition wall into two basins: 

s / Q{r + 5 + wf 
d ~\ 54>« 2 

In the latter equation the length of the sides of 
each basin are as 3 to 4. 

In these formulas: 

Q = capacity of reservoir to high-water line in cubic 
feet. 

d = depth of water in feet. 

r = cost of excavation in cents per square foot of 
area of finished reservoir. 

j = cost of floor of reservoir in cents per square 
foot. 

^ = cost in cents per square foot of the land upon 
which the reservoir is built. 


* Handbuch der Ingenieurwissenschaften, iii-i-ii. 







FIL TER ED - WA TER RESER VO IRS. 


26l 


m — a factor depending upon local conditions, 
being the cost per cubic foot of masonry mul¬ 
tiplied by the percentage of thickness of ma¬ 
sonry surrounding walls to their height. 

These formulas will also serve for rectangular 
covered reservoirs if the value of m is increased to 
correspond with the additional masonry in the piers, 
and if ^ is increased by the additional cost of the 
arches and earth covering over them and the piers 
supporting the roof. A few trials will quickly de¬ 
termine the economical depth. 

If the reservoir is covered with arches carried on 
piers its bottom area must be increased to compen¬ 
sate for their submerged volume. 

In case the reservoir is at a considerable eleva¬ 
tion above the works the economical depth is in¬ 
fluenced by the cost of pumping. If the bottom of 
the reservoir is established at the proper height to 
give the required pressure, the water-surface level 
will fluctuate with the draft, and it is, therefore, ap¬ 
parent that the depth will affect the cost of pump¬ 
ing. The economical depth may be found by ap¬ 
proximation from the formula,* 


^ j 5 _ <20 + * + w) _ 

6 m 12 mVQ' 

for an unroofed square reservoir, and 

4 /^5 _ <20 + s + w) _ 

m ''54 : 13 in VQ 

for an unroofed reservoir with one partition wall. 


* Frxihling, Handbuch der Ingenieurwissenschaften, 111-1-11. 









262 


WATER FILTRATION WORKS. 


Q — capacity of reservoir in cubic meters. 
d = depth of water in meters. 
r = cost of excavation per scp meter, 
s = cost of floor of reservoir per sq. meter. 
w — cost of land per sq. meter. 

m — a factor depending on local conditions, being 
the cost per cubic meter of masonry multiplied 
by the percentage of thickness of masonry 
surrounding walls to their height. 
k — the capitalized cost of both operating expenses 
and fixed charges per kilogram of water 
raised one meter high per second, and 
q = the average quantity of water to be pumped in 
litres per second. 

The value of d can be most easily found by succes¬ 
sive approximations. 

From an analysis of the formula it is easily seen 
that the influence of the depth upon the total cost, 
considering also the cost of pumping, will be greater 
the smaller the capacity of the reservoir relative to 
the daily delivery of the pumps. 

It frequently will occur that the shape of the 
ground available, the price of the land, the depth of 
the ground-water below the surface of the ground 
or the character of the subsoil will determine the 
size and depth of the reservoir, and the theoretical 
considerations for greatest economy will have to be 
modified to suit such conditions. 

Bottoms .—To secure a water-tight reservoir re¬ 
quires the greatest care in workmanship in all par¬ 
ticulars, and on such works only experienced and 


FILTERED-IVA 7 ER RESERVOIRS. 263 

competent workmen should be employed. Water¬ 
tight masonry, in the true sense of the word, does 
not exist, because all ordinary stones, mortars and 
bricks are permeable, to greater or lesser degrees, 
particularly under high pressures. A careful hand¬ 
ling of the materials will, however, reduce this leak¬ 
age to very small limits under the low heads usual 
in reservoirs of this class. The modern practice in 
the construction of masonry reservoirs tends tow¬ 
ards concrete, brick and stone structures plastered 
inside with cement mortar to secure tightness. The 
tendency is also to dispense with clay-puddle, al¬ 
though its use is quite common in American, English 
and some of the continental works, notably Ham¬ 
burg and Warsaw. 

It seems to be the general concensus of opinion, 
however, that for filtered-water reservoirs built upon 
sites where danger of contamination exists from 
ground-water a bed of carefully placed and com¬ 
pactly puddled clay is essential. The clay should 
preferably be mixed with about an equal volume 
of gravel or gravel and sand. In masonry of this 
class the stones should be rather small, sound, 
clean and have rough surfaces. The mortar should 
be made from a good strong Portland cement 
and sharp clean sand. All the bricks and stones 
should be moist when laid so as not to absorb 
the water from the mortar. They should be 
laid quickly, and all the joints should be filled 
completely. Concrete and range-rubble work are 
also used extensively, but in all these forms the 


264 WATER FILTRATION WORA'S. 

ability to resist leakage is derived largely by a plas¬ 
tering coat, on the walls and bottom, of Portland 
cement mortar from one eighth to three sixteenths of 
an inch thick rubbed down with a wooden float. The 
mortar should be mixed in the proportion of about 
one part of cement to two parts of sand, and a small 
quantity of thoroughly slaked lime may be added to 
increase the tightness and make it easier to smooth 
down. Finally, the walls should receive a wash of 
neat cement, applied with a broom or with a trowel, 
in the latter case being polished with a felt float. 
Polishing with a metal float is not satisfactory, be¬ 
cause the surface is apt to check in fine cracks when 
the cement has set. Upon the bottom a very thin 
layer of dry cement should be strewn by experienced 
men. This will adhere to the damp concrete bottom 
and make a very smooth hard surface, from which 
algae and other low plant-life and deposits may be 
readily washed. 

The bottoms of the basins sometimes require 
especial care in construction to make them water¬ 
tight. The site chosen for the filtered-water reser¬ 
voir for the Hamburg Water-works is adjacent to 
the old settling basins at Rothenburgsort, which 
were in service at the time the reservoir was being 
built. The soil was very unstable and great precau¬ 
tions were necessary to prevent the formation of 
springs by the excavation for the new reservoir. 
The excavation when finished and leveled off was 
lined with an 8-inch layer of well-compacted clay, 
upon which the concrete bottom of the reservoir was 


FIL TER ED - WA TER RESER VO IRS. 265 

laid. In the mass of the concrete, which was 20 
inches thick, was embedded a system of angle-irons 
crossing at right angles, and fastened to a heavy 
channel-iron running around the exterior edge. 
Upon this concrete floor the walls and piers are built 
which carry the roof. 

Walls .—In reservoirs built on a more or less com¬ 
pressible foundation, like clay-puddle, the side-walls 
and pillars should be carried up to a considerable 
height, in order that the settlement may cease be¬ 
fore laying the floor so that there may be no future 
settlement due to this cause. 

Where iron pipes pass through the masonry there 
is always difficulty in making tight joints. If there 
is danger of settlement of the walls the pipes should 
be carried through in openings considerably larger 
than they require, and all the settlement should be 
allowed to take place before the hole is filled up. 
To prevent leakage along the pipes a series of col¬ 
lars should be made on the part passing through the 
wall, and the hole should then be filled in with good, 
strong concrete, care being taken that the mortar is 
in perfect contact with the iron work and the 
masonry in all places. 

The side-walls of covered reservoirs are usually 
straight, designed as retaining walls to resist the ex¬ 
ternal pressure of the earth, with buttresses opposite 
the points from which arches spring, as in the reser¬ 
voir at Geneva, Switzerland. In some of the Ger¬ 
man and Italian reservoirs, however, they are made 
of an economical section designed to take the thrust 


266 


WATER FILTRATION WORKS. 


of the arch in a- curved line to the bottom of the 
foundation, as at Wiesbaden. Mr. Wm. H. Lindley, 
C.E., of Frankfort-on-the-Main, uses frequently a 
comparatively thin wall arched between heavy but¬ 
tresses spaced several feet apart in the length of the 
wall. The weight and load of each pier supporting 
the roof is distributed over a large area of the floor 
by inverted arches turned between the bottoms of the 
piers. 

Covers. —Filtered-water reservoirs should nearly 
always be roofed over to exclude light, to protect 
them from contamination and from the influence of 
temperature changes. The roofing may be done in a 
variety of ways. Groined, domical or cylindrical arches 
may be used for covering, as explained in chapter IV., 
or combination roofs of steel and concrete, or steel 
and brickwork may be employed advantageously. 
The roofs of filtered-water reservoirs should be made 
water-tight by a coating of asphalt and asbestic pa¬ 
per in two or three courses, with properly broken 
joints, and the water percolating down to the top 
should be carried away in a system of drain pipes. 
For this reason cylindrical arches are more suitable 
for reservoir-roofs than groined or domical struc- 
tures, as the drains for the roof may be laid in the 
valleys between the vaults. Light trussed roofs of 
iron or wood, covered with tin, slates or asphalt, may 
sometimes be sufficient where cheapness in first cost 
is a desideratum. Roofs of this kind are satis¬ 
factory for excluding light and affording plenty 
of ventilation in summer, but offer no consider- 


FILTERED-WATER RESERVOIRS . 267 

able protection against prolonged severe cold, un¬ 
less means are provided for heating the space 
above the water, by which the cost will be increased 
considerably. The Koenigsberg filters are covered 
with a trussed roof. 

There may be, occasionally, situations where, ow¬ 
ing to the constituents of the water, it would be un¬ 
suited, after filtration, to support vegetal growths. 
With such waters, possibly, covering of the filtered- 
water reservoirs would not be essential. This ques¬ 
tion is one that is occupying considerable attention 
on the part of biologists. In some cases, where 
proper conditions exist, the omission of covers over 
the reservoirs may assist in saving a community con¬ 
siderable expense. It is a point well worth exami¬ 
nation. 

If, instead of using piers or columns to support the 
roof, solid thin partition walls be built up from the 
bottom, dividing the reservoir into narrow parallel 
channels, the spaces being spanned with barrel 
arches, and each wall pierced with an opening at 
alternate ends, the water will be kept in constant 
motion and stagnation will be prevented. 

Ventilation .—There should be a^ number of venti¬ 
lation shafts placed over the reservoir to balance the 
air-pressures due to fluctuating water levels. The 
ventilators should be so constructed as to admit air, 
but exclude mice, toads, insects and flies. Light- 
shafts covered with heavy wire-glass should be built 
at convenient points to permit the cleaning of the 


268 


WATER FILTRATION WORKS. 


reservoir. They should be covered with an opaque 
lid of some sort when the reservoir is not in cleaning. 

A covering of earth two or three feet thick should 
be spread over the top of the masonry cover to pre¬ 
vent injury of the structure by frost and to prevent 
the water from freezing. 

It is desirable that the outlet for water from the 
reservoir should be at the opposite end of the reser¬ 
voir from the inlet, in order that all the water may 
circulate through the reservoir to avoid stagna¬ 
tion in parts distant from the outlet. The neces¬ 
sary valves should also be provided for draini g the 
reservoir and the different compartments, independ¬ 
ently, in case repairs should be necessary or cleaning 
desirable. Capacious over-flow pipes should likewise 
be provided. Under the drain pipe there should be a 
sump, into which all sediment and dirt may be 
pushed when cleaning. A large manhole over the 
sump will be necessary for the removal of this mat¬ 
ter, in buckets, by the workmen. 

Frequently it will also be desirable to have an au¬ 
tomatic depth-recording apparatus, when the reser¬ 
voir is at some distance from the works, which will 
indicate the state of the water in the reservoir upon 
a chart in the office of the works, or the pump-house, 
if desirable. 


INDEX. 


PAGB 

Aeration at Asbury Park. 4 

at Atlantic Highlands. 4 

effects of.4 t 42 

at Koenigsberg. 4 

Agitator, Jewell filter. 234 

Warren filter. 237 

Air-washing for rapid sand-filters. 237 

Albany, N. Y., cleaning settling basins. 71 

cost of filters. 177 

covers for filters. 127 

gravel layers in filters. 154 

sand-washers. 157 

> settling basins. 59 

Algae growths, effects on filters at Poughkeepsie. 188 

Antwerp. 189 

Allegheny River, turbidity of. 34 

Altona, amount of sediment collected. 66 

scraping filters. 186 

settling basins.46, 50 

Aluminum sulphate, action of. 201 

absorption by clay. 209 

corresponds to alkalinity of water. 204 

effect on color.207, 250 

public health. 203 

quality. 225 

American filters. 75 

Anaboena. 189 

Analysis of sand. 84 

269 































270 


INDEX. 


PAGE 

Anderson process.26, 249 

Anderson, Wm. vii 

Antwerp, algae growths on filters. 189 

amount of sediment collected. 66 

filters. 26 

regulating apparatus. 163 

intake for. 28 

settling basins.45, 50, 61 

studies of organisms in filters. 188 

water-supply... 28 

Anklamm. vii 

Arad, Hungary, Worms filters. 255 

Arnheim circular reservoir. 256 

Asbury Park water-supply. 4 

Ashland, Wis., cost of filters. 178 

filter-plant. 124 

Asterionella in Brooklyn water.... 189 

removal of. 5 

Atlantic Highlands water-supply. 4 

Automatic regulating apparatus for slow sand-filters. 168 


Bacteria, effects of sedimentation on 

in underdrains.. 

Bacterial efficiency. 

purification. 

Bailey, Geo. I. . . 

Baroda settling basins. 

Barus, Carl. 

Beer, M. 

Berlin, covers for filters. 

filters, regulating apparatus 
frequency of scraping filters 

filtration studies. 

intake for.. 

loss of head. 

plan of Lake Muggel filters.. 

rate of filtration. 

sand-washer. 

quality of water.. 

Bertschinger, A. >M 


. 6 

. 81 

. 81 

. 81 

.vii, 183 

. 50 

. 40 

. vii 

.101, 127 

. 164 

. 186 

. 97 

. 30 

. 9 i 

. 114 

. 93 

.157, 197 

. 2 

• • 

mmitmiMin VU 









































INDEX. 271 

VAGH 

Boston, protection of water-supply. 23 

reduction of organisms in water-mains. .. 9 

Boulogne-sur-Seine, Anderson process. 250 

Brooklyn, asterionella in water. 5 

Bradford, cost of cleaning water-mains. 11 

Brown, Andrew. 40 

Prof. C. C. 42 

Bristol, cost of cleaning water-mains. 11 

Buffalo, intake for. 24 

Burton, Prof. W. K. 163, 172 

Chemicals, use of, to aid sedimentation. 41 

Choisy-le-Roi, Anderson process. 250 

Chicago, intake for. 24 

Cincinnati, O., experiment station.vii, 25, 37, 39, 41, 91 

Clark, H. W., sedimentation. 40 

stored nitrogen in slow sand-filters. 87 

Cleaning water-mains.10, 11 

Cleveland, intake for. 24 

typhoid fever and rainfall. 18 

Coagulant, composition. 201 

effect on efficiency. 201 

ferric hydrate.26, 202, 249 

introduction into water. 225 

quantity required .203, 205 

measuring-tanks.227, 228 

mixing-tanks. 226 

piping for. 231 

pump. 230 

quantity required at Cincinnati. 206 

Louisville. 206 

Pittsburgh. 206 

Providence. 205 

time of admission. 207 

objects.... . 208 

time necessary for.207, 209 

Columbus, O., typhoid fever and rainfall. 18 

Color, failure of ferric hydrate to remove it. 203 

removal of, by alum.204, 207 

Combinations of rapid and slow sand-filters.. 132, 247 










































272 


V 

INDEX. 

PAGE 

Conclusions. 246 

Continental gravity filter. 220 

Controller for rapid sand-filters. 231 

Covers for filters, Berlin. 127 

effect in summer. 198 

winter. 198 

effect on frequency of scraping. 187 

Koenigsberg. 101 

protection from ice.101, 119, 120 

Crenothrix in Lawrence filters. 184 

Damages for pollution of water-supply. 15 

Danbury, Ct., sewage-pollution. 13 

Darjeeling, India, Pasteur filter plant. 250 

Deep wells, N. J., removal of iron. 4 

Delaware River, filters at Torresdale. 55 

sediment. 38 

Denbeigh, cost of cleaning water-mains. 11 

Depth-recording apparatus for reservoirs. 268 

Detroit, pollution of water.23, 24 

typhoid fever. x8 

Double filtration. 200 

Dresden, quality of water. 2 

Drown, Thos. M. v j 

Dumfries, cost of cleaning water-mains.„ u 

Durham, cost of cleaning water-mains..'. u 

East Albany rapid sand-filter plant. 220 

East Jersey Water Co. 229 

Edinburgh filters. j5 t 

protection of water-supply. xy 

sand-washers. 

Elbe, turbidity of. ^7 

Electric-light plants for filters. 

Exeter, cost of cleaning water-mains. u 

Ferric hydrate coagulant.26, 203 o •<. 

Filtered water, deteriorates in storage. 

Filtered-water reservoir bottoms. 

Berlin. 

capacity. 257 








































INDEX. 


273 


PAGE 

Filtered-water reservoir, circulation in. 257 


covers. 266 

depth. 260 

Hamburg. 264 

location. 256 

shape. 256 

ventilation. 267 

walls. 265 

Fire-reserve. 259 

Fischer filters.26, 255 

Flad, Edward.vii, 37, 33 

Fouling of water-mains. 9 

Fowler, Chas. E. 188 

Frankfort-on-Main, covered reservoir.52, 257 

Frankland, Grace. 79 

p - F .42, 79 

Freezing, effect on water . 12 

Freuhling, Prof.49, 50, 260, 261 

Fuller, Geo. W. 


26, 35. 37. 9*. 2o 5> 207, 209, 210, 211, 213, 214, 215, 244, 245 


Garonne River, turbidity.35, 37, 64, 65 

Geneva reservoir. 265 

Gill, Henry C. 164 

Glasgow, protection of water-supply. 17 

Gravel layers, slow sand-filters.142, 153 

Gray, S. M..19, 55 

Guisborough, cleaning water-mains. 11 


Hague, quality of water at. 2 

Halifax, cost of cleaning mains . 11 

Hamburg, filtered-water reservoir.258, 264 

growths in filters.... 188 

intake. 30 

loss of head. 97 

Mager scrapers. 19S 

rate of filtration. 93 

regulator.•. . 165 

settling basins.49, 50, 53, 56, 66 

Hardness of water. . 205 






































274 


INDEX. 


Hazen, Allen. 

Hemlock Lake, protection of supply 

Hering, Rudolph. 

Holman, M. L. 

Hooker, E. H. 

Hudson River, turbidity.. 

Human faeces, fertilizer ... -. 

Hygienic efficiency, definition. 


PAGE 

vi, 35, 36, 84, 119, 167, 205 

. 22 

.19, 35 , 55 , 119 

. 43 

."35 

. 35 

. 22 

. 81 


Ice on open filters. 198 

Hamburg. 198 

Poughkeepsie. 188 

Ilion, N. Y., regulating apparatus. 163 

Incrustation in pipe lines. 9 

Intake, Antwerp. 28 

Berlin. 30 

Buffalo. 24 

Hamburg. 30 

Shanghai. 29 

St. Louis. 33 

stable banks below floods. 30 

above floods. 29 

Zurich. 25 

Intermittent filters.82, 99 

Iron, removal by aeration. 4 

Jackson, D. D. 9 

Janowski. 6 

Jewell filter. 219 

Jordan, Edwin O. 79 

Kemna, Ad. 188 

Kirkwood, James P. 165 

Knowles, Morris. vii 

Koenigsberg, covered filters.101, 267 

regulating apparatus. 163 

water-supply. 4 

Lake St. Clair, pollution. 23 

Lake supplies, protection. 23 

Lanark, cost of cleaning mains. II 

Lancaster, cost of cleaning mains. 11 








































INDEX. 275 

PAGE 

Lawrence, Mass., clogging of filters. 184 

Lawrence experiment station.81, 83, 85, 87, 90, 92, 95, 97 

scraping filters. 185 

Lead-poisoning. r o 

Leeds, Prof. Albert R.■. 5 

Legal protection of water-supplies. 13 

Light, effect of, on sedimentation. 40 

Lime, use of, to aid sedimentation. 41 

used with soft water before coagulation. 204 

Lindley, W. H...vii, 52, 72, 169, 266 

Liverpool, protection of supply. 17 

London, regulating apparatus. 161 

settling basin.47, 50, 61 

Loss of head. 90 

Berlin. 91 

Hamburg. 91 

Louisville, coagulant. 205 

coagulant absorbed by clay. 209 

experiment station...vi, 25, 37 

plans for rapid sand-filters. 217 

quality of water. 2 

typhoid fever and rainfall. 18 

Mager scraper, Hamburg. 198 

Maignen filters.26, 255 

Manchester, protection of supply. 17 

settling basins. 62 

Mansergh, James. 17 

Mass. State Board of Health vi, 40, 79, 84, 92, 96, 97, 144, 146, 184 

McMath, R E. 37 

McMillan, Hon. James. 35 

Mechanical filters. 75 

Merrimac River, turbidity. 35 

Meyer, F. Andreas.vii, 166 

Mill acts. 13 

Mississippi River, turbidity...34, 36, 37, 38, 64 

Missouri River, turbidity.37, 51 

Modified English filters . 26 

Mud-deposits in reservoirs. 6 

Munich, quality of water. 2 








































2 j6 


INDEX. 


r AGE 

Nethe River. 28 

New Britain, sewage pollution. 13 

New Orleans experiment station. 25 

Newport, cost of cleaning mains. 11 

New York City, protection of water-supply.14, 17, 18 

N. Y. Continental, Jewell, Filtration Co.vii, 237 

N. Y. sectional-wash gravity filter . 225 

pressure filter. 226 

Nitrifying organism. 79 

Nyack filters, cost. 178 

Odors, removal of. 42 

Ohio River, turbidity.34, 39 

Omagh, cost of cleaning mains. 11 

Omaha, Neb., settling basins. 56 

Organisms, growths in Antwerp filters. 188 

Hamburg filters... 188 

Osaka, Japan, filter-regulating apparatus. 172 

Oswestry, cost of cleaning mains. 11 

Pail system. 22 

Parmelee, Chas. L. 237 

Pasteur filters.26, 250 

Paterson, typhoid fever and rainfall. 18 

Per capita water-consumption. 103 

Peter, M.vii, 169 

Pflugge. 97 

Philadelphia, cost of reservoirs. 63 

experiment station.vii, 25 

mud-deposits in mains. 9 

rapid-filter plant proposed on Schuylkill. 241 

regulating apparatus. 170 

water-supply report.;g, 55 

Piefke. ^ 

Pipes affected by alum solution. 204 

Pittsburgh, effect of trailing. 215 

experiment station.vi, 25, 243, 255 

quantity of coagulant. 205 

quality of water. 2 

typhoid fever and rainfall. 18 








































INDEX. 277 

PAGE 

Plagge.,. 81 

Pollution of water-supplies, damages for. 15 

Detroit. 18 

Port Huron. 23 

Potomac River, turbidity of. 35 

Poughkeepsie, algae growths on filters. 188 

Proskauer. 97 

Protection of water-supplies. 13 

Boston. 23 

Edinburgh. 17 

Glasgow. 17 

lake supplies. 23 

Liverpool. 17 

Manchester. 17 

New York. 13 

Rochester. 22 

Providence experiment station.vi, 25 

Public health, effect of alum on. 203 

Purification of water by natural agencies. 3 

Rainfall and typhoid fever. 18 

Rapid sand-filters, air-washing. 237 

advantages. 246 

combinations with slow.122, 247 

construction. 217 

Continental gravity. 220 

cost. 238 

effect of filtering medium. 210 

loss of head.^13 

rate of filtration. 211 

trailing. 215 

washing. 214 

essential to use coagulant. 248 

gravity and pressure. 217 

Jewell gravity. 219 

labor for operation. 243 

lost sand. 243 

Louisville rectangular. 219 

necessity for services of chemist. 248 

New York sectional wash gravity. 225 

pressure. 220 










































278 


INDEX . 


PAGE 

Rapid sand-filters, operation. 242 

patents. 217 

period of time between washings. 242 

plant at East Albany. 220 

rectangular, advantages. 241 

time necessary for washing. 243 

wash-water.237, 244 

washing arrangements. 234 

washing with caustic soda. 215 

wasting filtered water. 215 

Weston’s Automatic Controller. 231 

Rapid sand-filtration.76, 201 

introduction of chemicals. 225 

Rate of filtration, Berlin. 93 

Hamburg. 93 

Reading, Mass., removal of iron. 4 

Refilling slow sand-filters. 100 

Regulating apparatus, Berlin. 164 

Edinburgh. 161 

Hamburg. 165 

Ilion. 163 

Koenigsberg. 163 

London. 161 

Osaka.i. 172 

Philadelphia. 170 

Stralau. 161 

Tokio . 172 

Tome Institute. 171 

Warsaw. 168 

Yokohama. 162 

Zurich. 168 

Reinisch. 98 

Reservoirs, cost. 63 

for filtered water. 256 

bottoms. 262 

capacity. 257 

circulation in. 257 

covers. 266 

depth. 260 

walls. 265 










































INDEX. 279 

PAGE 

Reservoirs, preparation of site.6, 20 

protection to surface supplies. ig 

Richards, Ellen H. yg 

Rochester, N. Y., protection of supply. 22 

Rotterdam, intake.._. 46 

settling basins. 61 

Rupel River. 28 

Sacramento River, turbidity. 64 

Sand.146, 149 

effective size. 84 

lost in washing slow filters. 198 

rapid filters. 243 

transportation to washers. 190 

uniformity coefficient. 84 

Sand-washers. 157, 159 

washing. 154 

cost. 190 

Sandhurst, Vic., lime as coagulant. 41 

Sanitary precautions during reservoir construction. 21 

San Francisco, typhoid and rainfall. 18 

Scarborough, cost of cleaning mains. n 

Schuylkill River. 38 

Scraping slow sand-filters.97, 98, 180 

Altona. 186 

Berlin. 186 

cost. 183 

effect of covers on. 187 

frequency. 185 

in freezing weather. 198 

Lawrence . 185 

under ice, Hamburg. 198 

quantity of sand removed. 185 

Zu rich.186, 187 

Sedden, James A. 4 ° 

Se-diment, amount to be expected.34, 36, 64, 65, 66 

removal of.60, 61 

Sedimentation, continuous vs. intermittent.60, 64, 73 

effect of light. 40 

on bacteria. 5 









































280 


INDEX. 


PAG B 

Sedimentation, purification by. 3 , 33 

results of. 41 

use of chemicals.41, 204 

lime. 41 

Seeding beds. 184 

Settling basins, arrangements for cleaning. 56 

capacity. 46 

cleaning.66, 68, 71 

construction. 53 

cost. 62 

of cleaning. 72 

depth. 47 

design. 45 

form. 51 

Hamburg.49, 50, 53, 56, 66 

inlets and outlets. 52 

length. 48 

London.47, 50, 61 

Manchester. 62 

Omaha. 56 

operation...63, 66, 67 

regulating apparatus.56, 59 

roofing. 61 

Shanghai, intake. 29 

settling basins.50, 61 

Simpson, James. . 161 

Slow sand-filters, action of. 80 

advantages. 246 

automatic regulators. 168 

bottoms. X34 

combined with rapid. 247 

construction. Ix ^ 

cost . 174 

covering. I20 

depth. 117 

designing. I03 

drainage of roof. I30 

efficiency. go 

excess area required. IO y 

filtering sand. I4 6, 149 










































INDEX . 


28 l 


PAGE 

Slow sand-filters, gravel.142, 153 

location. 113 

operation. 179 

refilling after scraping.100, 199 

shape. 115 

stored nitrogen and bacteria. 89 

underdrains. 139 

ventilation and lighting. 133 

Slow sand-filtration. 76 

effect of compacting sand. 84 

effect of depth of sand. 86 

water. 93 

loss of head. 90 

rate of filtration. 93 

influence of age of filter. 96 

character of sand.84, 85 

water. 82 

theory. 77 

Soda-ash. 204 

Soft water, soda-ash used with. 204 

lime used with. 204 

Somersworth, N. H., covered filter.129, 146, 153 

Sterilization by vegetation.3, 188 

Strainers. 26 

Stralau filter regulators. 161 

Stralsunder, covered filters. 122 

St. Louis, intake for. 33 

settling basins.40, 42, 43, 48, 50, 53, 55, 61, 65, 72 

Stream-pollution, Danbury, Ct. 13 

New Britain, Ct. 13 

Waterbury, Ct. 13 

Streams, permissible pollution. 13 

self-purification.12, 188 

Storage, effects on filtered water.5, 258, 266 

surface water.5, 19 

Strohmeyer, Otto. 188 

Surface film, slow filters. 97 

Surface washings, effect on water. 17 

Swamps, drainage of. 21 

Synedra. 189 










































282 


INDEX. 


PAGE 

Temperature, effect on sedimentation. 40 

slow sand-filtration. 100 

Tidal streams, intakes. 2S 

Tokio, filters, regulating apparatus. 172 

Toledo, O., typhoid fever and rainfall. 18 

Tome Institute filters, regulating apparatus. 171 

Tramways for sand haulage. 134 

Turbidity.34, 3^ 

and quantity of coagulant required. 20t 

Delaware River. 38 

difficulty of removing. ... 204 

Elbe River. 37 

Garonne River.35, 37, 64, 65 

Hudson River. 35 

Merrimac River. 35 

Mississippi River.34, 3 6 , 37, 3$, 64 

Ohio River.34, 39 

Potomac River. 35 

removal by coagulant. 204 

Sacramento River. 64 

Schuylkill River. 38 

Typhoid fever and quality of water. 2 

rainfall. 18 

water-supply. 1 

Ulverston, cost of cleaning water-mains. 11 

Underdrains, bacteria in. 81 

slow sand-filters. 139 

Vicksburg, settling basins. 50, 64 

Volontat, M. R. de.35, 64 

Waelhem, intake for Antwerp. 28 

Warsaw, regulating apparatus. 168 

Washington, D. C.vi, 35 

quality of water. 2 

Waste reduction. 104 

Wasting effluents, rapid sand-filters.215, 245 

slow sand-filters. 100 

Waterbury, stream-pollution. 13 







































INDEX. 283 

PAGE 

Water consumption per capita. 103 

Water-mains, cleaning. 9 

cost of. 10 

incrustation. 9 

Water and public health. 1 

purification by natural agencies. 3 

Water-supplies, damages for pollution.... 15 

legal protection. 13 

provisions for betterment. 14 

Wells, deep. 4 

Weston, E. B. 205, 209, 242, 243, 245 

Wheeler, Wm.vii, 124 

Whipple, Geo. C.6, 9, 37, 189 

Whitehaven, cost of cleaning water-mains. 11 

Williams, G. S. 23 

Wilson, Jos. M.19, 55 

Winds, effect on sedimentation. 39 

Winogradsky. 79 

Worms filters.26, 250 

construction of plates. 255 

regulating apparatus. 172 

Yang-tse-kiang River, intake for Shanghai. 29 

Yokohama filters, regulating apparatus. 162 

Zurich, automatic regulating apparatus. 168 

filters. 138 

intake. 25 

rate of filtration. 94 > 101 

scraping filters. 186, 187 

































SHORT-TITLE CATALOGUE 

OF THE 

PUBLICATIONS 

OF 

JOHN WILEY & SONS, 

New York. 

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London: CHAPMAN & HALL, Limited. 

ARRANGED UNDER SUBJECTS. 


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4 


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00 

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75 

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50 

00 

OO 

25 

50 

OO 

OO 

OO 


50 

OO 

OO 

OO 

50 

60 

OO 

25 

50 

OO 

OO 

50 

OO 

OO 

50 

OO 

OO 

OO 


50 

OO 

50 

OO 











































* Reisig’s Guide to Piece-dyeing.8vo, 25 cs 

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Gore’s Elements of Geodesy.8vo, 2 50 

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5 


















































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Siebert and Biggin’s Modern Stone-cutting and Masonry.8vo, 1 5° 

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Sheep, 6 50 

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Sheep, 5 50 

Law of Contracts. 8vo, 3 00 

Warren’s Stereotomy—Problems in Stone-cutting.8vo, 2 50 

Webb’s Problems in the Use and Adjustment of Engineering Instruments. 

i6mo, morocco, 1 25 

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Wilson’s Topographic Surveying.8vo, 3 50 

BRIDGES AND ROOFS. 

Boiler’s Practical Treatise on the Construction of Iron Highway Bridges. .8vo, 2 00 

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Foster’s Treatise on Wooden Trestle Bridges.4to, 5 00 

Fowler’s Coffer-dam Process for Piers.:.8vo, 2 50 

Ordinary Foundations.8vo, 3 50 

Greene’s Roof Trusses.*..8vo, 1 25 

Bridge Trusses.8vo, 2 50 

Arches in Wood, Iron, and Stone.8vo, 2 50 

Howe’s Treatise on Arches.8vo, 4 00 

Design of Simple Roof-trusses in Woed and Steel.8vo, 2 00 

Johnson, Bryan, and Turneaure’s Theory and Practice in the Designing of 

Modern Framed Structures.SmdTl 4to, 10 00 

Merriman and Jacoby’s Text-book on Roofs and Bridges: 

Part I.—Stresses in Simple Trusses. . .8vo, 2 50 

Part II.—Graphic Statics.8vo, 2 50 

Part IH.—Bridge Design. 4th Edition, Rewritten.8vo, 2 50 

Part IV.—Higher Structures.8vo, 2 50 

Morison’s Memphis Bridge.4to, 10 00 

Waddell’s De Pontibus, a Pocket-book for Bridge Engineers... i6mo, morocco, 3 00 

Specifications for Steel Bridges...i2mo, 1 25 

Wood’s Treatisfe on the Theory of the Construction of Bridges and Roofs.8vo, 2 00 
Wright’s Designing of Draw-spans: 

Part I. —Plate-girder Draws./.8vo# 2 50 

Part II.—Riveted-truss and Pin-connected Long-span Draws.8vo, 2 50 

Two parts in one volume.8vo, 3 50 

fi 














































HYDRAULICS. 

Bazin’s Experiments upon the Contraction of the Liquid Vein Issuing from an 

Orifice. (Trautwine.).8vo, 2 00 

Bovey’s Treatise on Hydraulics. 8vo, 5 00 

Church’s Mechanics of Engineering.8vo, 6*oo 

Diagrams of Mean Velocity of Water in Open Channels.paper, 1 50 

Coffin’s Graphical Solution of Hydraulic Problems.x6mo, morocco, 2 50 

Flather’s Dynamometers, and the Measurement of Power.i2mo, 3 00 

Folwell’s Water-supply Engineering.8vo, 4 00 

Frizell’s Water-power.8vo, 5 00 

Fuertes’s Water and Public Health...i2mo, 1 50 

Water-filtration Works.i2mo, 2 50 

Ganguillet and Kutter’s General Formula for the Uniform Flow of Water in 

Rivers and Other Channels. (Hering and Trautwine.).8vo, 4 00 

Hazen’s Filtration of Public Water-supply.8vo, 3 00 

Hazlehurst’s Towers and Tanks for Water-works.8vo, 2 50 

Herschel’s 115 Experiments on the Carrying Capacity of Large, Riveted, Metal 

Conduits.8vo, 2 00 

Mason’s Water-supply. (Considered Principally from a Sanitary Stand¬ 
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Merriman’s Treatise on Hydraulics, gth Edition, Rewritten.. ... .8vo, 5 00 

• Michie’s Elements of Analytical Mechanics.8vo, 4 o» 

Schuyler’s Reservoirs for Irrigation, Water-power, and Domestic Water- 

supply.Large 8vo, 5 00 

•* Thomas and Watt’s Improvement of Riyers. (Post., 44 c. additional), 4to, 6 00 

Turneaure and Russell’s Public Water-supplies.8vo, 5 00 

Wegmann’s Desien and Construction of Dams.4to, 5 00 

Water-supply of the City of New York from 1658 to 1895.4to, 10 00 

Weisbach’s Hydraulics and Hydraulic Motors. (Du Bois.).8vo, 5 00 

Wilson's Manual of Irrigation Engineering.Small 8vo, 4 00 

Wolff’s Windmill as a Prime Mover.8vo, 3 00 

Wood’s Turbines.8vo, 2 50 

Elements of Analytical Mechanics.8vo, 3 00 

MATERIALS OP ENGINEERING. 

Baker’s Treatise on Masonry Construction.8vo, 5 00 

Roads and Pavements.8vo, 5 00 

Black’s United States Public Works.Oblong 4to, 5 00 

Bovey’s Strength of Materials and Theory of Structures.8vo, 7 50 

Burr’s Elasticity and Resistance of the Materials of Engineering. 6th Edi¬ 
tion, Rewritten.8vo, 7 50 

Byrne’s Highway Construction.8vo, 5 00 

Inspection of the Materials and Workmanship Employed in Construction. 

i6mo, 3 00 

Church’s Mechanics of Engineering.8vo, 6 00 

Du Bois’s Mechanics of Engineering. Vol. I.Small 4to, 7 50 

Johnson’s Materials of Construction.Large 8vo, 6 00 

Fowler’s Ordinary Foundations.8vo, 3 50 

Keep’s Cast Iron.8vo, 2 50 

Lanza’s Applied Mechanics.8vo, 7 50 

Martens’s Handbook on Testing Materials. (Henning.) 2 vols.8vo, 7 50 

Merrill’s Stones for Building and Decoration.8vo, 5 00 

Merriman’s Text-book on the Mechanics of Materials.8vo, 4 00 

Strength of Materials.i2mo, 1 00 

Metcalf’s Steel. A Manual for Steel-users.nmo, 2 00 

Patton’s Practical Treatise on Foundations.8vo, 5 00 

Richey’s Handbook for Building Superintendents of Construction. (In press.) 
Rockwell’s Roads and Pavements in France. i2mo, 1 25 

7 















































Sabin’s Industrial and Artistic Technology of Paints and Varnish.Svo, 

Smith’s Materials of Machines. ..i2mo, 

Snow’s Principal Species of Wood.8vo, 

Spalding’s Hydraulic Cement.i2mo, 

Text-book on Roads and Pavements.i2mo, 

Taylor and Thompson’s Treatise on Concrete, Plain and Reinforced. {In 
press.) 

Thurston’s Materials of Engineering. 3 Parts.8vo, 

Part 1.—Non-metallic Materials of Engineering and Metallurgy.8vo, 

Part II.—Iron and Steel.8vo, 

Part III.—A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents.8vo, 

Thurston’s Text-book of the Materials of Construction.8vo, 

Tillson’s Street Pavements and Paving Materials.8vo, 

Waddell’s De Pontibus. (A Pocket-book for Bridge Engineers.). . i6mo, mor., 

Specifications for Steel Bridges.nmo, 

Wood’s (De V.) Treatise on the Resistance of Materials, and an Appendix on 

the Preservation of Timber.8vo, 

Wood’s (De V.) Elements of Analytical Mechanics. 8vo, 

Wood’s (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and 
Steel.8 vo, 

RAILWAY ENGINEERING. 


Andrews’s Handbook for Street Railway Engineers.3x5 inches, morocco, 

Berg’s Buildings and Structures of American Railroads.4to, 

Brooks’s Handbook of Street Railroad Location.i6mo, morocco, 

Butts’s Civil Engineer’s Field-book.i6mo, morocco, 

Crandall’s Transition Curve.i6mo, morocco, 

Railway and Other Earthwork Tables.8vo, 

Dawson’s “Engineering” and Electric Traction Pocket-book. i6mo, morocco, 
Dredge’s History of the Pennsylvania Railroad: (1879).Paper, 

* Drinker’s Tunneling, Explosive Compounds, and Rock Drills, 4to, half mor., 

Fisher’s Table of Cubic Yards.Cardboard, 

Godwin’s Railroad Engineers’ Field-book and Explorers’ Guide.... i6mo, mor., 

Howard’s Transition Curve Field-book.i6mo, morocco, 

Hudson’s Tables for Calculating the Cubic Contents of Excavations and Em¬ 
bankments.8vo, 

Molitor and Beard’s Manual for Resident Engineers.i6mo, 

Nagle’s Field Manual for Railroad Engineers.i6mo, morocco, 

Philbrick's Field Manual for Engineers.i6mo, morocco, 

Searles’s Field Engineering.i6mo, morocco, 

Railroad Spiral.i6mo, morocco, 

Taylor’s Prismoidal Formulae and Earthwork.8vo, 

* Trautwine’s Method ot Calculating the Cubic Contents of Excavations and 

Embankments by the Aid of Diagrams.8vo, 

The Field Practice of Laying Out Circular Curves for Railroads. 

i2mo, morocco, 

Cross-section Sheet.Paper, 

Webb’s Railroad Construction. 2d Edition, Rewritten.i6mo, morocco, 

Wellington’s Economic Theory of the Location of Railways.Small 8vo, 

DRAWING. 

Barr’s Kinematics of Machinery,.8vo, 

* Bartlett’s Mechanical Drawing.8vo, 

* “ Abridged Ed.8vo, 

Coolidge’s Manual of Drawing.8vo, paper, 

Coolidge and Freeman’s Elements of General Drafting for Mechanical Engi¬ 
neers.Oblong 4to. 

Durley’s Kinematics of Machines.8vo, 


3 00 

1 00 
3 50 

2 00 
2 00 


8 00 

2 00 

3 50 

2 50 
5 00 

4 00 

3 00 

1 25 

2 00 

3 00 

4 OO 


I 25 
5 00 

1 50 

2 50 
1 50 

1 50 
5 00 
5 00 

25 00 
25 

2 50 
1 50 

I OO 
I OO 

3 00 
3 00 
3 00 
1 50 

1 50 

2 OO 

2 50 
25 
5 OO 
5 00 

2 50 

3 00 
1 50 

1 00 

2 50 

4 OQ 


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Hill's Text-book on Shades and Shadows, and Perspective.8vo, 

Tamison's Elements of Mechanical Drawing.8vo, 

Jones’s Machine Design: 

Part I.—Kinematic&*of Machinery.8vo, 

Part II.—Form, Strength, and Proportions of Parts.8vo, 

MacCord’s Elements of Descriptive Geometry.8vo, 

Kinematics; or. Practical Mechanism.8vo, 

Mechanical Drawing.4to, 

Velocity Diagrams.8vo, 

Mahan’s Descriptive Geometry and Stone-cutting.8vo, 

Industrial Drawing. (Thompson.).8vo, 

Moyer’s Descriptive Geometry. (Zn press.) 

Reed’s Topographical Drawing and Sketching.4to, 

Reid’s Course in Mechanical Drawing.8vo, 

Text-book of Mechanical Drawing and Elementary Machine Design. .8vo, 

Robinson’s Principles of Mechanism., .8vo, 

Schwamb and Merrill’s Elements of Mechanism.8vo, 

Smith’s Manual of Topographical Drawing. (McMillan.).8vo, 

Warren’s Elements of Plane and Solid Free-hand Geometrical Drawing. . nmo, 

Drafting Instruments and Operations.i2mo, 

Manual of Elementary Projection Drawing.i2mo, 

Manual of Elementary Problems in the Linear Perspective of Form and 

Shadow.12 mo, 

Plane Problems in Elementary Geometry.i2mo, 

Primary Geometry.i2mo, 

Elements of Descriptive Geometry, Shadows, and Perspective.8vo, 

General Problems of Shades and Shadows...8vo 

Elements of Machine Construction and Drawing.8vo, 

Problems, Theorems, and Examples in Descriptive Geometry.8vo, 

Weisbach’s Kinematics and the Power of Transmission. (Hermann and 

Klein.).8vo, 

Whelpley’s Practical Instruction in the Art of Letter Engraving.i2mo, 

Wilson’s (H. M.) Topographic Surveying.8vo, 

Wilson’s (V. T.) Free-hand Perspective. 8vo, 

Wilson’s (V. T.) Free-hand Lettering.8vo, 

Woolf’s Elementary Course in Descriptive Geometry.Large 8vo, 

ELECTRICITY AND PHYSICS. 

Anthony and Brackett’s Text-book of Physics. (Magie.).Small 8vo, 

Anthony’s Lecture-notes on the Theory of Electrical Measurements. . . . i2mo, 

Benjamin’s History of Electricity..8vo, 

Voltaic Cell.8vo, 

Classen’s Quantitative Chemical Analysis by Electrolysis. (Boltwood.). 8vo, 

Crehore and Squier’s Polarizing Photo-chronograph.8vo, 

Dawson’s “Engineering” and Electric Traction Pocket-book. . i6mo, morocco, 
Dolezalek’s Theory of the Lead Accumulator (Storage Battery). (Von 

Ende.).i2mo, 

Duhem’s Thermodynamics and Chemistry. (Burgess.).8vo, 

Flather’s Dynamometers, and the Measurement of Power.i2mo, 

Gilbert’s De Magnete. (Mottelay.). 8v0 > 

Hanchett’s Alternating Currents Explained. i2mo, 

Hering’s Ready Reference Tables (Conversion Factors).i6mo, morocco, 

Holman’s Precision of Measurements.8vo, 

Telescopic Mirror-scale Method, Adjustments, and Tests.Large 8vo, 

Landauer's Spectrum Analysis. (Tingle.)... .8vo, 

Le Chatelier’s High-temperature Measurements. (Boudouard—Burgess. )nmo 
Ltfb’* Electrolysis and Electrosynthesis of Organic Compounds. (Lorenz.) t2mo, 

9 


2 OO 
2 50 


i 50 
3 oo 
3 oo 
5 oo 
oo 
50 
50 
50 


5 oo 

2 oo 

3 oo 
3 oo 
3 oo 
2 50 
i oo 
i 25 
i 50 


oo 

25 

75 

50 

oo 

50 

50 


5 oo 

2 OO 

3 50 

2 50 
i oo 

3 oo 


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3 oo 
3 oo 
5 oo 


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* Lyons's Treatise on Electromagnetic Phenomena. Vols. I. and II. 8vo, each, 6 oo 

* Michie. Elements of Wave Motion Relating to Sound and Light.8vo, 4 00 

Niaudet’s Elementary Treatise on Electric Batteries. (FishDack.).i2mo, 2 50 

* Rosenberg’s Electrical Engineering. (Haldane Gee—Kinzbrunner.)... . 8 vo, 1 50 

Ryan, Norris, and Hoxie’s Electrical Machinery. VoL L.8vo, 2 50 

Thurston’s Stationary Steam-engines.8vo, 2 50 

* Tillman’s Elementary Lessons in Heat.8vo, 1 50 

Tory and Pitcher’s Manual of Laboratory Physics.Small 8vo, 2 00 

Hike’s Modern Electrolytic Copper Refining ... 8 vo, 3 00 

LAW. 

* Davis’s Elements of Law. 8vo, 2 50 

* Treatise on the Military Law ot United States...8vo, 700 

* Sheep, 7 50 

Manual for Courts-martial.i6mo, morocco, 1 50 

Wait’s Engineering and Architectural Jurisprudence.8vo, 6 00 

Sheep, 6 50 

Law of Operations Preliminary to Construction in Engineering and Archi¬ 
tecture. 8 vo, 5 00 

Sheep, 5 50 

Law of Contracts.8vo, 3 00 

Winthrop’s Abridgment of Military Law.i2mo, 2 50 

MANUFACTURES. 

Bernadou’s Smokeless Powder—Nitro-cellulose and Theory of the Cellulose 

Molecule.nmo, 2 50 

Bolland’s Iron Founder.i2mo, 2 50 

’’The Iron Founder,” Supplement.i2mo, 2 50 

Encyclopedia of Founding and Dictionary of Foundry Terms Used in the 

Practice of Moulding.i2tno, 3 00 

Eissler’s Modern High Explosives.8vo, 4 00 

Effront’s Enzymes and their Applications. (Prescott.).8vo 3 00 

Fitzgerald’s Boston Machinist.i8mo, 1 00 

Ford’s Boiler Making for Boiler Makers.i8mo, 1 00 

Hopkins’s Oil-chemists’ Handbook.8vo, 3 00 

Keep’s Cast Iron.8vo, 2 50 

Leach’s The Inspection and Analysis of Food with Special Reference to State 
Control. (In preparation.) 

Matthews’s The Textile Fibres.8vo, 3 50 

Metcalf’s SteeL A Manual for Steel-users.i2mo, 2 00 

Metcalfe’s Cost of Manufactures—And the Administration of Workshops, 

Public and Private.8vo, 5 00 

Meyer’s Modern Locomotive Construction.4to, 10 00 

Morse’s Calculations used in Cane-sugar Factories.i6mo, morocco, 1 50 

* Reisig’s Guide to Piece-dyeing.8vo, 25 00 

Sabin’s Industrial and Artistic Technology of Paints and Varnish.8vo, 3 00 

Smith’s Press-working of Metals.8vo, 3 00 

Spalding’s Hydraulic Cement.i2mo, 2 00 

Spencer’s Handbook for Chemists of Beet-sugar Houses.i6mo, morocco, 3 00 

Handbook for Sugar Manufacturers and their Chemists... i6mo morocco, 2 00 
Taylor and Thompson’s Treatise on Concrete, Plain and Reinforced. (In 
press.) 

Thurston’s Manual of Steam-boilers, their Designs, Construction and Opera¬ 
tion.8vo, s 00 

* Walke’3 Lectures on Explosives.8vo, 4 00 

West’s American Foundry Practice.i2mo, 2 50 

Moulder’s Text-book.. 250 

10 . 









































Wolff’s Windmill as a Prime Mover.8vo, 300 

Woodbury’s Fire Protection of Mills.8vo, 2 50 

Wood’s Rustless Coatings: Corrosion and Electrolysis of Iron and Steel.. .8vo, 4 00 

MATHEMATICS. 

Baker’s Elliptic Functions.8vo, 1 50 

* Bass’s Elements of Differential Calculus.i2mo, 4 00 

Briggs’s Eiements of Plane Analytic Geometry.i2mo, 1 00 

Compton’s Manual of Logarithmic Computations.i2mo, 1 50 

Davis’s Introduction to the Logic of Algebra.8vo, 1 50 

* Dickson’s College Algebra.Large i2mo, 1 50 

* Answers to Dickson’s College Algebra.8vo, paper, 25 

* Introduction to the Theory of Algebraic Equations .Large 12mo, 1 25 

Halsted’s Elements of Geometry.8vo, 1 75 

Elementary Synthetic Geometry.8vo, 1 50 

Rational Geometry.i2mo, 

* Johnson’s (J. B.) Three-place Logarithmic Tables: Vest-pocket size, paper, 15 

100 copies for 5 00 

* Mounted on heavy cardboard, 8 X10 inches, 25 

10 copies for 2 00 

Johnson’s (W. W.) Elementary Treatise on Differential Calculus. . .Small 8vo, 3 00 

Johnson’s (W. W.) Elementary Treatise on the Integral Calculus. .Small 8vo, 1 50 

Johnson’s (W. W.) Curve Tracing in Cartesian Co-ordinates.i2mo, 1 00 

Johnson’s (W. W.) Treatise on Ordinary and Partial Differential Equations. 

Small 8vo, 3 50 

Johnson’s (W. W.) Theory of Errors and the Method of Least Squares. . i2mo, 1 50 

* Johnson’s (W. W.) Theoretical Mechanics.i2mo, 3 00 

Laplace’s Philosophical Essay on Probabilities. (Truscott and Emory.) nmo, 2 00 

* Ludlow and Bass. Elements of Trigonometry and Logarithmic and Other 

Tables.8vo, 3 00 

Trigonometry and Tables published separately. Each, 2 00 

* Ludlow’s Logarithmic and Trigonometric Tables.8vo, 1 00 

Maurer’s Technical Mechanics.8vo, 4 00 

Merriman and Woodward’s Higher Mathematics.8vo, 5 00 

Merriman’s Method of Least Squares.8vo, 2 00 

Rice and Johnson’s Elementary Treatise on the Differential Calculus.Sm., 8vo, 3 00 

Differential and Integral Calculus. 2 vols. in one.Small 8vo, 2 50 

Wood’s Elements of Co-ordinate Geometry.8vo, 2 00 

Trigonometry: Analytical, Plane, and Spherical.i2mo, 1 00 

MECHANICAL ENGINEERING. 

MATERIALS OF ENGINEERING, STEAM-ENGINES AND BOILERS. 

Bacon’s Forge Practice.i2mo, 1 yn 

Baldwin’s Steam Heating for Buildings.12mo, 2 50 

Barr’s Kinematics of Machinery.8vo, 2 50 

* Bartlett’s Mechanical Drawing.8vo, 3 00 

* “ " “ Abridged Ed.8vo, 1 50 

Benjamin’s Wrinkles and Recipes.i2mo, 2 00 

Carpenter’s Experimental Engineering.8vo, 6 00 

Heating and Ventilating Buildings.8vo, 4 00 

Cary’s Smoke Suppression in Plants using Bituminous CoaL (In prep¬ 
aration.) 

Clerk’s Gas and Oil Engine...Small 8vo, 4 00 

Coolidge’s Manual of Drawing.8vo, paper, 1 00 

Coolidge and Freeman’s Elements of General Drafting for Mechanical En¬ 
gineers.Oblong 4to, 2 §q 

u 





































Cromwell’s Treatise on Toothed Gearing.... i2mo i 

Treatise on Belts and Pulleys...i2mo, i 

Durley’s Kinematics of Machines.8vo, 4 

Flather’s Dynamometers and the Measurement of Power.i2mo, 3 

Rope Driving.. 2 

Gill’s Gas and Fuel Analysis for Engineers.i2mo, 1 

Hall's Car Lubrication.i2mo, 1 

Hering’s Ready Reference Tables (Conversion Factors).i6mo, morocco, 2 

Hutton’s The Gas Engine.8vo, 5 

Jamison’s Mechanical Drawing.8vo, 2 

Jones’s Machine Design: 

Part I.—Kinematics of Machinery. 8vo, 1 

Part II.—Form, Strength, and Proportions of Parts.8vo, 3 

Kent’s Mechanical Engineer’s Pocket-book.i6mo, morocco, 5 

Kerr’s Power and Power Transmission.8vo, 2 

Leonard’s Machine Shops, Tools, and Methods, (/n preaa.) 

MacCord’s Kinematics; or, Practical Mechanism.8vo, 5 

Mechanical Drawing.4to, 4 

Velocity Diagrams.8vo, 1 

Mahan’s Industrial Drawing. (Thompson.)......8vo, 3 

Poole’s Calorific Power of Fuels.8vo, 3 

Reid’s Course in Mechanical Drawing.8vo, 2 

Text-book of Mechanical Drawing and Elementary Machine Design.. 8vo, 3 

Richards’s Compressed Air.i2mo, 1 

Robinson’s Principles of Mechanism.8vo, 3 

Schwamb and Merrill’s Elements of Mechanism.8vo, 3 

Smith’s Press-working of Metals. 8vo, 3 

Thurston’s Treatise on Friction and Lost Work in Machinery and Mill 

Work.8vo, 3 

Animal as a Machine and Prime Motor, and the Laws of Energetics. nmo, 1 

Warren’s Elements of Machine Construction and Drawing.8sro, 7 

Weisbach’s Kinematics and the Power of Transmission. Herrmann— 

Klein.).8vo, 5 

Machinery of Transmission and Governors. (Herrmann—Klein.). .8vo 5 

Hydraulics and Hydraulic Motors. (Du Bois.).8vo, 5 

Wolff’s Windmill as a Prime Mover.8vo, 3 

Wood’s Turbines. 8vo, 2 

MATERIALS OF ENGINEERING. 

Bovey’s Strength of Materials and Theory of Structures.8vo, 7 

Burr’s Elasticity and Resistance of the Materials of Engineering. 6th Edition 

Reset..'.8 vo, 7 

Church’s Mechanics of Engineering.8vo, 6 

Johnson’s Materials of Construction.Large 8vo, 6 

Keep’s Cast Iron.8vo, 2 

Lanza’s Applied Mechanics.8vo, 7 

Martens’s Handbook on Testing Materials. (Henning.).8vo, 7 

Merriman’s Text-book on the Mechanics of Materials. .8vo, 4 

Strength of Materials. i2mo, 1 

Metcalf’s Steel. A Manual for Steel-users.i2mo 2 

Sabin’s Industrial and Artistic Technology of Paints and Varnish.8vo, 3 

Smith's Materials of Machines.12mo, 1 

Thurston’s Materials of Engineering.. vols., Svo, 8 

Part II.—Iron and Steel.8vo, 3 

Part HI.—A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents.. 2 

Text-book of the Materials of Construction.. 5 

12 


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Wood’s (De V.) Treatise on the Resistance of Materials and an Appendix on 

the Preservation of Timber. 8vo, 2 00 

Wood’s (De V.> Elements of Analytical Mechanics.8vo, 3 00 

Wood’s (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and Steel. 

8vo, 4 00 

STEAM-ENGINES AND BOILERS. 

Carnot’s Reflections on the Motive Power of Heet. (Thurston.).i2mo, 1 50 

Dawson’s “Engineering” and Electric Traction Pocket-book. .i6mo, mcr., 5 00 

Ford’s Boiler Making for Boiler Makers.i8mo, 1 00 

Goss’s Locomotive Sparks..8vo, 200 

Hemenway’s Indicator Practice and Steam-engine Economy.i2mo, 2 00 

Hutton’s Mechanical Engineering of Power Plants.8vo, 5 00 

Heat and Heat-engines.8vo. 5 00 

Kent’s Steam-boiler Economy.8vo, 4 00 

Kneass’s Practice and Theory of the Injector.8vo, 1 50 

Mac Cord’s Slide-valves.8vo, 2 00 

Meyer’s Modern Locomotive Construction.4 to, 10 00 

Peabody’s Manual of the Steam=engine Indicator.i2mo, 1 50 

Tables of the Properties of Saturated Steam and Other Vapors.8vo, 1 00 

Thermodynamics of the Steam-engine and Other Heat-engines.8vo, 5 00 

Valve-gears for Steam-engines.8vo, 2 50 

Peabody and Miller’s Steam-boilers.8vo. 4 00 

Pray’* Twenty Years with the Indicator.Large 8vo, 2 50 

Pupln’s Thermodynamics of Reversible Cycles in Gases and Saturated Vapors. 

(Osterberg.).i2mo, 1 25 

Reagan’s Locomotives : Simple, Compound, and Electric.i2mo, 2 50 

Rontgen’s Principles of Thermodynamics. (Du Bois.).8vo, 5 00 

Sinclair’s Locomotive Engine Running and Management.i2mo, 2 00 

Smart’s Handbook of Engineering Laboratory Practice.i2mo, 2 50 

Snow’s Steam-boiler Practice.8vo, 3 00 

Spangler’s Valve-gears. 8vo, 2 50 

Notes on Thermodynamics...i2mo, 1 00 

Spangler, Greene, and Marshall’s Elements of Steam-engineering.8vo, 3 00 

Thurston’s Handy Tables.8vo, 1 50 

Manual of the Steam-engine.2 vols.. 8vo, 10 00 

Parti.—History, Structuce, and Theory.8vo, 6 00 

Part H.;—Design, Construction, and Operation.8vo, 6 00 

Handbook of Engine and Boiler Trials, and the Use of the Indicator and 

the Prony Brake.8vo, 5 00 

Stationary Steam-engines..•.8vo, 2 50 

Steam-boiler Explosions in Theory and in Practice.i2mo, 1 50 

Manual of Steam-boilers, Their Designs, Construction, and Operation. 8vo, 5 00 

Weisbach’s Heat, Steam, and Steam-engines. (Du Bois.).8vo, 5 00 

Whitham’s Steam-engine Disign.8vo, 5 00 

Wilson’s Treatise on Steam-boilers. (Flather.).i6mo, 250 

Wood’s Thermodynamics Heat Motors, and Refrigerating Machines... .8vo, 4 00 

MECHANICS AND MACHINERY. 

Barr’s Kinematics of Machinery.8vo, 2 50 

Bovey’s Strength of Materials and Theory of Structures.8vo, 7 50 

Chase’s The Art of Pattern-making.i2mo, 2 50 

Chordal.—Extracts from Letters.i2mo, 2 00 

Church’s Mechanics of Engineering.8vo, 6 00 


13 












































Church’s Notes and Examples in Mechanics.8vo, 2 oo 

Compton’s First Lessons in Metal-working.i2mo, i 50 

Compton and De Groodt’s The Speed Lathe. .nmo, 1 50 

Cromwell’s Treatise on Toothed Gearing.i2mo, 1 50 

Treatise on Belts and Pulleys.i2mo, 1 50 

Dana’s Text-book of Elementary Mechanics for the Use of Colleges and 

Schools.i2mo, 1 50 

Dingey's Machinery Pattern Making.i2mo> 2 00 

Dredge’s Record of the Transportation Exhibits Building of the World’s 

Columbian Exposition of 1893.4to half morocco, 5 00 

Du Bois’s Elementary Principles of Mechanics: 

VoL I.—Kinematics.8vo, 3 5° 

Vol. II.—Statics.8vo, 4 00 

Vol. III.—Kinetics.8vo, 3 50 

Mechanics of Engineering. Vol. I...Small 4to, 7 50 

VoL IL.Small 4to, 10 00 

Durley’s Kinematics of Machines .8vo, 4 00 

Fitzgerald’s Boston Machinist.i6mo, 1 00 

Flather’s Dynamometers, and the Measurement of Power.izmo, 3 00 

Rope Driving.i2mo, 2 00 

Goss’s Locomotive Sparks.8vo, 2 00 

Hall’s Car Lubrication.i2mo, 1 00 

Holly’s Art of Saw Filing.i8mo, 75 

* Johnson’s (W. W.) Theoretical Mechanics.i2mo, 3 00 

Johnson’s (L. J.) Statics by Graphic and Algebraic Methods.8vo, 2 00 

Jones’s Machine Design: 

Part I.—Kinematics of Machinery.8vo, 1 50 

Part II.—Form, Strength, and Proportions of Parts.8vo, 3 00 

Kerr’s Power and Power Transmission.8vo, 2 00 

Lanza’s Applied Mechanics.8vo, 7 50 

Leonard s Machine Shops, Tools, and Methods, (/n press.) 

MacCord’s Kinematics; or. Practical Mechanism.8vo, 5 00 

Velocity Diagrams..8vo, 1 50 

Maurer’s Technical Mechanics.8vo, 400 

Merriman’s Text-book on the Mechanics of Materials.8vo, 4 00 

* Michie’s Elements of Analytical Mechanics.8vo, 4 00 

Reagan’s Locomotives: Simple, Compound, and Electric.iamo, 2 50 

Reid’s Course in Mechanical Drawing.8vo, 2 00 

Text-book of Mechanical Drawing and Elementary Machine Design. .8vo, 3 00 

Richards’s Compressed Air.i2mo, 1 50 

Robinson’s Principles of Mechanism.*. .8vo, 3 00 

Ryan, Norris, and Hoxie’s Electrical Machinery. Vol. 1.8vo, 2 50 

Schwamb and Merrill’s Elements of Mechanism.8vo, 3 00 

Sinclair’s Locomotive-engine Running and Management.i2mo, 2 00 

Smith’s Press-working of Metals.8vo, 3 00 

Materials of Machines.i2mo, 1 00 


Thurston’s Treatise on Friction and Lost Work in Machinery and Mill 

Work...8vo, 3 00 

Animal as a Machine and Prime Motor, and the Laws of Energetics. i2mo, 1 00 

Warren’s Elements of Machine Construction and Drawing.8vo, 7 50 

Weisbach’s Kinematics and the Power of Transmission. (Herrmann— 

Klein.). 8vo, 5 00 

Machinery of Transmission and Governors. (Herrmann—Klein.).8vo, 5 00 

Wood’s Elements of Analytical Mechanics.8vo, 3 00 

Principles of Elementary Mechanics.i2mo, 1 25 

Turbines.8vo, 2 50 

The World’s Columbian Exposition of 1893.4to, 1 00 

14 


















































METALLURGY. 

Bgleston’s Metallurgy of Silver, Gold, and Mercury: 

VoL I.—Silver. 8vo, 7 *>d 

VoL II.—Gold and Mercury.8vo, 7 50 

** Iles’s Lead-smelting. (Postage 9 cents additional.).i2mo, 2 50 

Keep’s Cast Iron.8vo, 2 50 

Kunhardt’s Practice of Ore Dressing in Europe. 8vo, 1 50 

Le Chatelier’s High-temperature Measurements. (Boudouard—Burgess.). nmo, 3 00 

Metcalf’s SteeL A Manual for Steel-users.i2mo, 2 00 

Smith’s Materials of Machines.12020, 1 00 

Thurston’s Materials of Engineering. In Three Parts.8vo, 8 00 

Part II.—Iron and Steel.8vo, 3 50 

Part HI.—A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents.8vo, 2 50 

Dike’s Modern Electrolytic Copper Refining.8vo, 3 00 

MINERALOGY. 

Barringer’s Description of Minerals of Commercial Value. Oblong, morocco, 2 50 

Boyd’s Resources of Southwest Virginia.8vo, 3 00 

Map of Southwest Virginia.Pocket-book form, 2 00 

Brush’s Manual of Determinative Mineralogy. (Penfield.).8vo, 4 00 

Chester’s Catalogue of Minerals.8vo, paper, 1 00 

Cloth, 1 25 

Dictionary of the Names of Minerals.8vo, 3 50 

Dana's System of Mineralogy.Large 8vo, half leather, 12 50 

First Appendix to Dana’s New “System of Mineralogy.”... .Large 8vo, 1 00 

Text-book of Mineralogy.8vo, 4 00 

Minerals and How to Study Them...i2mo, 1 50 

Catalogue of American Localities of Minerals.Large 8vo, 1 00 

Manual of Mineralogy and Petrography.i2mo, 2 00 

Douglas’s Untechnical Addresses on Technical Subjects...i2mo, 1 00 

Eakle’s Mineral Tables.8vo, 1 25 

Egleston’s Catalogue of Minerals and Synonyms.8vo, 2 50 

Hussak’s The Determination of Rock-torming Minerals. (Smith.) Small 8vo, 2 00 

Merrill’s Non-metallic Minerals: Their Occurrence and Uses..8vo, 4 00 

* Penfield’s Notes on Determinative Mineralogy and Record of Mineral Tests. 

8vo, paper, o 50 

Rosenbusch’s Microscopical Physiography of the Rock-making Minerals. 

(Iddings.).8vo, 5 00 

* Tillman’s Text-book of Important Minerals and Docks.8vo, 2 00 

Williams’s Manual of Lithology. 8vo, 3 00 

MINING. 

Beard’s Ventilation of Mines.l2mo, 2 50 

Boyd’s Resources of Southwest Virginia.8vo, 3 00 

Map of Southwest Virginia.Pocket-book form, 2 00 

Douglas’s Untechnical Addresses on Technical Subjects.12010, 1 00 

* Drinker’s Tunneling, Explosive Compounds, and Rock Drills. 

4to, half morocco, 25 00 

Eissler’s Modern High Explosives.8vo, 4 00 

Fowler’s Sewage Works Analyses.i2mo, 2 00 

Goodyear’s Coal-mines of the Western Coast of the United States.i2mo, 2 50 

Ihiseng’s Manual of Mining....8vo, 4 00 

** Iles’s Lead-smelting. (Postage 9c. additionaL).i2mo, 2 50 

Kunhardt’s Practice of Ore Dressing in Europe.8vo, 1 50 

O’Driscoll’s Notes on the Treatment of Gold Ores.8vo, 2 00 

* Walke’s Lectures on Explosives.8vo, 4 00 

Wilson’s Cyanide Processes.xamo, 1 50 

Chlorination Process.iamo, 1 50 


15 












































SANITARY SCIENCE. 

Folwell’s Sewerage. (Designing, Construction, and Maintenance.).8vo, 

Water-supply Engineering.8vo, 

Fuertes’s Water and Public Health.nmo, 

Water-filtration Works.nmo, 

Gerhard’s Guide to Sanitary House-inspection.i6mo, 

Goodrich’s Economical Disposal of Town’s Refuse.Demy 8vo, 

Hazen’s Filtration of Public Water-supplies.8vo, 

Leach’s The Inspection and Analysis of Food with Special Reference to State 

Control.8vo, 

Mason’s Water-supply. (Considered Principally from a Sanitary 

point.) 3d Edition, Rewritten.8vo, 

Examination of Water. (Chemical and Bacteriological.).nmo, 

Merriman’s Elements of Sanitary Engineering.8vo, 

Ogden’s Sewer Design.nmo, 

Prescott and Winslow’s Elements of Water Bacteriology, with Special Reference 



2 

00 


I 

25 


3 

00 


4 

00 


I 

50 

. . nmo, 

2 

50 


I 

00 

0 

> 

00 

>> 

6 

3 

50 


3 

00 

to State 


7 

50 

Stand- 


4 

00 


1 

25 


2 

00 


2 

00 


Richards’s Cost of Food. 


point. 


Von Behring’s Suppression of Tuberculosis. 



1 

25 


1 

50 


1 

00 


1 

00 

Stand- 




2 

00 


1 

50 


3 

50 


5 

00 


1 

00 


3 

50 


1 

50 


MISCELLANEOUS. 

Emmons’s Geological Guide-book of the Rocky Mountain Excursion of the 

International Congress of Geologists.Large 8vo, 

Ferrel’s Popular Treatise on the Winds.8vo, 

Haines’s American Railway Management.nmo 

Mott’s Composition, Digestibility, and Nutritive Value of Food. Mounted chart. 

Fallacy of the Present Theory of Sound.i6mo, 

Ricketts’s History of Rensselaer Polytechnic Institute, 1824-1894. Small 8vo, 

Rostoski’s Serum Diagnosis. (Bolduan.).nmo, 

Rotherham’s Emphasized New Testament.Large 8vo, 

Steel’s Treatise on the Diseases of the Dog.8vo, 

Totten’s Important Question in Metrology.8vo, 

The World’s Columbian Exposition of 1893.4to, 

Von Behring’s Suppression of Tuberculosis. (Bolduan.).nmo, 

Worcester and Atkinson. Small Hospitals, Establishment and Maintenance, 
and Suggestions for Hospital Architecture, with Plans for a Small 
Hospital.nmo, 

HEBREW AND CHALDEE TEXT-BOOKS. 

Green’s Grammar of the Hebrew Language.8vo, 

Elementary Hebrew Grammar.nmo, 

Hebrew Chrestomathy.8vo, 

Gesenius’s Hebrew and Chaldee Lexicon to the Old Testament Scriptures. 

(Tregelles.).Small 4to, half morocco, 

Letterii’Is Hebrew Bible. 8vo, 


50 

00 

50 

25 

00 

00 

00 

00 


3 50 
2 50 
I 00 
I 00 


I 25 


3 00 

1 25 

2 00 

5 00 
2 25 


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